{"id":1643,"date":"2019-08-08T12:39:51","date_gmt":"2019-08-08T16:39:51","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-12-skeletal-system\/"},"modified":"2024-12-02T12:25:51","modified_gmt":"2024-12-02T17:25:51","slug":"unit-12-skeletal-system","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/chapter\/unit-12-skeletal-system\/","title":{"raw":"Unit 12: The Skeletal System","rendered":"Unit 12: The Skeletal System"},"content":{"raw":"<div class=\"unit-12:-skeletal-system\">\r\n<div class=\"textbox shaded\">\r\n\r\n<strong>Unit outline<\/strong>\r\n\r\n<a href=\"#12A\"><strong>A. Bone Tissue and the Skeletal System<\/strong><\/a>\r\n\r\n<a href=\"#12A1\"><strong>Part 1:<\/strong> The Functions of the Skeletal System<\/a>\r\n<ul>\r\n \t<li><a href=\"#12A1a\">Support, movement, and protection<\/a><\/li>\r\n \t<li><a href=\"#12A1b\">Mineral storage, energy storage, and hematopoiesis<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#12A2\"><strong>Part 2: <\/strong>Bone Classification<\/a>\r\n\r\n<a href=\"#12A3\"><strong>Part 3:<\/strong> Bone Structure<\/a>\r\n<ul>\r\n \t<li><a href=\"#12A3a\">Gross anatomy of bone<\/a><\/li>\r\n \t<li><a href=\"#12A3b\">Bone cells and tissues<\/a><\/li>\r\n \t<li><a href=\"#12A3c\">Compact and spongy bone<\/a><\/li>\r\n \t<li><a href=\"#12A3d\">Blood and nerve supply<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#12A4\"><strong>Part 4: <\/strong>Bone Formation and Development<\/a>\r\n<ul>\r\n \t<li><a href=\"#12A4a\">Cartilage templates<\/a><\/li>\r\n \t<li><a href=\"#12A4b\">Intramembranous ossification<\/a><\/li>\r\n \t<li><a href=\"#12A4c\">Endochondral ossification<\/a><\/li>\r\n \t<li><a href=\"#12A4d\">How bones grow in length<\/a><\/li>\r\n \t<li><a href=\"#12A4e\">How bones grow in diameter<\/a><\/li>\r\n \t<li><a href=\"#12A4f\">Bone remodeling<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#12A5\"><strong>Part 5:<\/strong> Fractures<\/a>\r\n\r\n&nbsp;\r\n\r\n<a href=\"#12B\"><strong>B. Skeletal Anatomy<\/strong><\/a>\r\n\r\n<a href=\"#12B1\"><strong style=\"text-align: initial;font-size: 1em\">Part 1: The<\/strong> <strong style=\"text-align: initial;font-size: 1em\">Axial Skeleton<\/strong><\/a>\r\n<ul>\r\n \t<li><a href=\"#12B1a\">The Skull<\/a><\/li>\r\n \t<li><a href=\"#12B1b\">The Vertebral Column<\/a><\/li>\r\n \t<li><a href=\"#12B1c\">The Thoracic Cage<\/a><\/li>\r\n<\/ul>\r\n<a href=\"#12B2\"><strong>Part 2. The Appendicular Skeleton<\/strong><\/a>\r\n<ul>\r\n \t<li><a href=\"#12B2a\">The Pectoral Girdle<\/a><\/li>\r\n \t<li><a href=\"#12B2b\">Bones of the Upper Limb<\/a><\/li>\r\n \t<li><a href=\"#12B2c\">The Pelvic Girdle and Pelvis<\/a><\/li>\r\n \t<li><a href=\"#12B2d\">Bones of the Lower Limb<\/a><\/li>\r\n<\/ul>\r\n<h2><a href=\"#P\">Practice Questions<\/a><\/h2>\r\n<\/div>\r\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><strong>Learning Objectives<\/strong><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nAt the end of this unit, you should be able to:\r\n<p class=\"hanging-indent\"><strong>I.<\/strong> Describe the functions of the skeletal system and the five basic shapes of human bones.<\/p>\r\n<p class=\"hanging-indent\"><strong>II.<\/strong> Describe the structure and histology of the skeletal system.<\/p>\r\n<p class=\"hanging-indent\"><strong>III. <\/strong>Define and identify the following parts of a long bone: diaphysis, epiphysis, metaphysis, articular cartilage, periosteum, medullary cavity, and endosteum.<\/p>\r\n<p class=\"hanging-indent\"><strong>IV. <\/strong>Compare the composition and function of compact bone versus spongy bone.<\/p>\r\n<p class=\"hanging-indent\"><strong>V. <\/strong>Define ossification, compare intramembranous ossification with endochondral ossification, describe how a long bone grows in length and width, and specify how various factors might affect the rate of ossification and, by extension, the height of a mature individual.<\/p>\r\n<p class=\"hanging-indent\"><strong>VI. <\/strong>Specify the components of the axial and appendicular skeletons, describe the general function of each skeleton, and name and describe the principal components of the axial skeleton.<\/p>\r\n<p class=\"hanging-indent\"><strong>VII. <\/strong>Describe the structure and function of a typical vertebra and explain how these differ in the case of the atlas and axis.<\/p>\r\n<p class=\"hanging-indent\"><strong>VIII. <\/strong>Describe the components and functions of the pectoral girdle and the pelvic girdle.<\/p>\r\n<p class=\"hanging-indent\"><strong>IX.<\/strong> Specify all bones and structures in the human skeleton covered in this Unit.<\/p>\r\n<p class=\"hanging-indent\"><strong>X. <\/strong>Describe the differences between the pelvis of a human female and that of a human male.<\/p>\r\n<p class=\"hanging-indent\"><strong>XI. <\/strong>Describe the major differences between the skeleton of an infant and that of an adult.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><strong>Learning Objectives and Guiding Questions<\/strong><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nAt the end of this unit, you should be able to complete all the following tasks, including answering the guiding questions associated with each task.\r\n<p class=\"hanging-indent\"><strong>I.<\/strong> Describe the functions of the skeletal system and the five basic shapes of human bones.<\/p>\r\n\r\n<ol>\r\n \t<li>Specify the ways that the skeletal system functions in the human body.<\/li>\r\n \t<li>The main common functions of all components of the human skeletal system are \u201cprotection\u201d and \u201csupport\u201d. Based on the material that follows in this Unit, select several examples of individual components (including both bone and cartilage examples) and describe how they serve each of these two functions.<\/li>\r\n \t<li>Name, describe, and provide one example of each of the five different shapes of human bones.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>II.<\/strong> Describe the structure and histology of the skeletal system.<\/p>\r\n\r\n<ol>\r\n \t<li class=\"no-indent\">Based on previously covered material and the information in this Unit, describe each of the different cell types found in cartilage and bone. For each cell type, identify:\r\n<ul>\r\n \t<li class=\"no-indent\">Where in the body, and from which type of cell, it arose.<\/li>\r\n \t<li class=\"no-indent\">Where it normally resides in the body, as specifically as possible.<\/li>\r\n \t<li class=\"no-indent\">What its main function is, and how (briefly) it serves that function.<\/li>\r\n \t<li class=\"no-indent\">What happens to the cell if the matrix that surrounds it calcifies.<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li class=\"no-indent\">Based on previously covered material and the information in this Unit, compare and contrast the components of cartilage matrix and bone matrix, explaining the differences in the physical characteristics of cartilage and bone.<\/li>\r\n \t<li class=\"no-indent\">From what tissue type do bones and cartilage arise during early development? What other mature tissues arise from the same fetal tissue type?<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>III. <\/strong>Define and identify the following parts of a long bone: diaphysis, epiphysis, metaphysis, articular cartilage, periosteum, medullary cavity, and endosteum.<\/p>\r\n\r\n<ol>\r\n \t<li>Create a fully-labelled diagram of a typical long bone, showing the main external and internal features and identifying all the main tissue types found in a long bone.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>IV. <\/strong>Compare the composition and function of compact bone versus spongy bone.<\/p>\r\n\r\n<ol>\r\n \t<li class=\"hanging-indent\">Compare and contrast compact bone and spongy bone, in terms of the following characteristics:\r\n<ul>\r\n \t<li style=\"list-style-type: none\">\r\n<ul>\r\n \t<li class=\"hanging-indent\">The tissue type and cell type found in each type of bone.<\/li>\r\n \t<li class=\"hanging-indent\">The arrangement of tissue and\/or cells in each type of bone.<\/li>\r\n \t<li class=\"hanging-indent\">The location of each within a bone.<\/li>\r\n \t<li class=\"hanging-indent\">The function of each type of bone.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li class=\"hanging-indent\">Use annotated diagrams to compare and contrast the internal structure of an osteon with that of a trabecula.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>V. <\/strong>Define ossification, compare intramembranous ossification with endochondral ossification, describe how a long bone grows in length and width, and specify how various factors might affect the rate of ossification and, by extension, the height of a mature individual.<\/p>\r\n\r\n<ol>\r\n \t<li class=\"hanging-indent\">Explain in detail the processes of:\r\n<ul>\r\n \t<li class=\"hanging-indent\">Intramembranous ossification<\/li>\r\n \t<li class=\"hanging-indent\">Endochondral ossification<\/li>\r\n \t<li class=\"hanging-indent\">Growth in length of a long bone<\/li>\r\n \t<li class=\"hanging-indent\">Growth in width of a long bone<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li class=\"hanging-indent\">Compare and contrast the processes of intramembranous ossification and endochondral ossification.<\/li>\r\n \t<li class=\"hanging-indent\">Compare and contrast the processes of endochondral ossification and lengthwise growth of a long bone.<\/li>\r\n \t<li class=\"hanging-indent\">Compare and contrast the processes of intramembranous ossification and widthwise growth of a long bone.<\/li>\r\n \t<li class=\"hanging-indent\">The height of an individual is largely determined by the rate of ossification prior to physical maturity. Briefly explain why this is so.<\/li>\r\n \t<li class=\"hanging-indent\">Based on information provided in this and other Units, briefly describe the effects you would expect to see, if any, on the height of an individual under the following conditions, and briefly explain your reasoning for each.\r\n<ul>\r\n \t<li class=\"hanging-indent\">Hypersecretion of growth hormone during development<\/li>\r\n \t<li class=\"hanging-indent\">Hyposecretion of growth hormone during development<\/li>\r\n \t<li class=\"hanging-indent\">Premature onset of puberty<\/li>\r\n \t<li class=\"hanging-indent\">Late onset of puberty<\/li>\r\n \t<li class=\"hanging-indent\">Shorter than average parents<\/li>\r\n \t<li class=\"hanging-indent\">Taller than average parents<\/li>\r\n \t<li class=\"hanging-indent\">Excessive caloric intake during development<\/li>\r\n \t<li class=\"hanging-indent\">Malnutrition during development<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<ol>\r\n \t<li class=\"hanging-indent\" style=\"list-style-type: none\"><\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>VI. <\/strong>Specify the components of the axial and appendicular skeletons, describe the general function of each skeleton, and name and describe the principal components of the axial skeleton.<\/p>\r\n\r\n<ol>\r\n \t<li class=\"hanging-indent\">List all the components of the axial skeleton.<\/li>\r\n \t<li class=\"hanging-indent\">List all the components of the appendicular skeleton.<\/li>\r\n \t<li class=\"hanging-indent\">Write one sentence that clearly describes and differentiates between the axial and appendicular skeletons.<\/li>\r\n \t<li class=\"hanging-indent\">Specify the main functions of the axial skeleton, and that of the appendicular skeleton. Explain how the overall shape of each skeleton is appropriate to its primary function.<\/li>\r\n \t<li>Describe the location of the following:\r\n<ul>\r\n \t<li>Xiphoid process of the sternum<\/li>\r\n \t<li>Mastoid process of the temporal bone<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Describe in general terms the location and function of the following:\r\n<ul>\r\n \t<li class=\"hanging-indent\">Hyoid bone<\/li>\r\n \t<li class=\"hanging-indent\">Incus, malleus, and stapes<\/li>\r\n \t<li class=\"hanging-indent\">Atlas<\/li>\r\n \t<li class=\"hanging-indent\">Axis<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>VII. <\/strong>Describe the structure and function of a typical vertebra and explain how these differ in the case of the atlas and axis.<\/p>\r\n\r\n<ol>\r\n \t<li class=\"hanging-indent\">Sketch a diagram of a typical vertebra, clearly showing and labelling all the following components:\r\n<ul>\r\n \t<li class=\"hanging-indent\">Body<\/li>\r\n \t<li class=\"hanging-indent\">Vertebral foramen<\/li>\r\n \t<li class=\"hanging-indent\">Transverse processes<\/li>\r\n \t<li class=\"hanging-indent\">Spinous process<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li class=\"hanging-indent\">Sketch a diagram of the atlas and of the axis, clearly showing and labelling the following components, where applicable:\r\n<ul>\r\n \t<li class=\"hanging-indent\">Body<\/li>\r\n \t<li class=\"hanging-indent\">Vertebral foramen<\/li>\r\n \t<li class=\"hanging-indent\">Transverse processes<\/li>\r\n \t<li class=\"hanging-indent\">Spinous process<\/li>\r\n \t<li class=\"hanging-indent\">Dens<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>VIII. <\/strong>Describe the components and functions of the pectoral girdle and the pelvic girdle.<\/p>\r\n\r\n<ol>\r\n \t<li class=\"hanging-indent\">List the bones that make up in the pectoral girdle. Identify each as being part of the appendicular or axial skeleton.<\/li>\r\n \t<li class=\"hanging-indent\">List the bones and cartilage that make up the pelvic girdle. Identify each as being part of the appendicular or axial skeleton.<\/li>\r\n \t<li class=\"hanging-indent\">Compare and contrast the location, structure, and function of the pectoral girdle and the pelvic girdle. What about them is similar? What differs?<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>IX.<\/strong> Specify all bones and structures in the human skeleton covered in this Unit.<\/p>\r\n\r\n<ol>\r\n \t<li>Locate and identify the following bones in a diagram of a human skeleton:\r\n<ul>\r\n \t<li>Frontal bone<\/li>\r\n \t<li>Parietal bone<\/li>\r\n \t<li>Temporal bone<\/li>\r\n \t<li>Occipital bone<\/li>\r\n \t<li>Mandible<\/li>\r\n \t<li>Maxilla<\/li>\r\n \t<li>Cervical vertebrae<\/li>\r\n \t<li>Thoracic vertebrae<\/li>\r\n \t<li>Lumbar vertebrae<\/li>\r\n \t<li>Sacrum<\/li>\r\n \t<li>Coccyx<\/li>\r\n \t<li>True ribs<\/li>\r\n \t<li>False ribs<\/li>\r\n \t<li>Floating ribs<\/li>\r\n \t<li>Sternum<\/li>\r\n \t<li>Clavicle<\/li>\r\n \t<li>Scapula<\/li>\r\n \t<li>Humerus<\/li>\r\n \t<li>Radius<\/li>\r\n \t<li>Ulna<\/li>\r\n \t<li>Carpals<\/li>\r\n \t<li>Metacarpals<\/li>\r\n \t<li>Phalanges<\/li>\r\n \t<li>Hip bone<\/li>\r\n \t<li>Femur<\/li>\r\n \t<li>Patella<\/li>\r\n \t<li>Tibia<\/li>\r\n \t<li>Fibula<\/li>\r\n \t<li>Tarsals<\/li>\r\n \t<li>Metatarsals<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t<li>Sketch a human skeleton from memory. Label all the large long bones, and all the visible cartilages. Check your sketch against your textbook and worksheet to see if you\u2019ve missed anything.<\/li>\r\n \t<li>By external examination (look and feel), determine the location of your own:\r\n<ul>\r\n \t<li class=\"hanging-indent\">Phalanges<\/li>\r\n \t<li class=\"hanging-indent\">Metacarpals and metatarsals<\/li>\r\n \t<li class=\"hanging-indent\">Carpals and tarsals<\/li>\r\n \t<li class=\"hanging-indent\">Humerus and femur<\/li>\r\n \t<li class=\"hanging-indent\">Patella<\/li>\r\n \t<li class=\"hanging-indent\">Ulna, radius, tibia, and fibula<\/li>\r\n \t<li class=\"hanging-indent\">True ribs, false ribs, and floating ribs<\/li>\r\n \t<li class=\"hanging-indent\">Sternum<\/li>\r\n \t<li class=\"hanging-indent\">Clavicle and scapula<\/li>\r\n \t<li class=\"hanging-indent\">Iliac crest of the hip bone<\/li>\r\n \t<li class=\"hanging-indent\">Maxilla and mandible<\/li>\r\n \t<li class=\"hanging-indent\">Frontal bone and occipital bone<\/li>\r\n \t<li class=\"hanging-indent\">Sacrum<\/li>\r\n \t<li class=\"hanging-indent\">Spinous process of a vertebra<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>X. <\/strong>Describe the differences between the pelvis of a human female and that of a human male.<\/p>\r\n\r\n<ol>\r\n \t<li>Describe the differences between an average male pelvis and an average female pelvis.<\/li>\r\n \t<li>Why are male and female pelves generally shaped differently? For each sex difference noted in the question above, briefly explain the functional relevance of that sex difference specifically.<\/li>\r\n<\/ol>\r\n<p class=\"hanging-indent\"><strong>XI. <\/strong>Describe the major differences between the skeleton of an infant and that of an adult.<\/p>\r\n\r\n<ol>\r\n \t<li>Describe the difference in tissue composition (relative amounts of different tissue types) of the skeleton of a child and that of an adult.<\/li>\r\n \t<li>Explain why the skeleton of a newborn contains more bones than that of an adult, by naming two examples of bones that are formed by fully fusing two or more pieces of bone tissue.<\/li>\r\n \t<li>Describe the difference in relative body proportions between the skeleton of an infant and that of an adult.<\/li>\r\n \t<li>Describe the differences between the skull of a newborn and that of an adult.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<h1 style=\"text-align: justify\"><strong><a id=\"12A\"><\/a>A. Bone Tissue and the Skeletal System<\/strong><\/h1>\r\n<p style=\"text-align: justify\">Your skeleton is a structure of living tissue that grows, repairs, and renews itself. The bones within it are dynamic and complex organs that serve a number of important functions, including some necessary to maintain homeostasis.<\/p>\r\n<p style=\"text-align: justify\">The skeletal system forms the rigid internal framework of the body. It consists of the bones, cartilages, and ligaments. Bones support the weight of the body, allow for body movements, and protect internal organs. Cartilage provides flexible strength and support for body structures such as the thoracic cage, the external ear, and the [pb_glossary id=\"2737\"]trachea[\/pb_glossary] and [pb_glossary id=\"2738\"]larynx[\/pb_glossary]. At joints of the body, cartilage can also unite adjacent bones or provide cushioning between them. [pb_glossary id=\"2735\"]Ligaments[\/pb_glossary] are the strong connective tissue bands that hold the bones at a moveable joint together and serve to prevent excessive movements of the joint that would result in injury. Providing movement of the skeleton are the muscles of the body, which are firmly attached to the skeleton via connective tissue structures called [pb_glossary id=\"2736\"]tendons[\/pb_glossary]. As muscles contract, they pull on the bones to produce movements of the body. Thus, without a skeleton, you would not be able to stand, run, or even feed yourself!<\/p>\r\n<p style=\"text-align: justify\">Each bone of the body serves a particular function, and therefore bones vary in size, shape, and strength based on these functions. For example, the bones of the lower back and lower limb are thick and strong to support your body weight. Similarly, the size of a bony landmark that serves as a muscle attachment site on an individual bone is related to the strength of this muscle. Muscles can apply very strong pulling forces to the bones of the skeleton. To resist these forces, bones have enlarged bony landmarks at sites where powerful muscles attach. This means that not only the size of a bone, but also its shape, is related to its function. Bones are also dynamic organs that can modify their strength and thickness in response to changes in muscle strength or body weight. Thus, muscle attachment sites on bones will thicken if you begin a workout program that increases muscle strength. Similarly, the walls of weight-bearing bones will thicken if you gain body weight or begin pounding the pavement as part of a new running regimen. In contrast, a reduction in muscle strength or body weight will cause bones to become thinner. This may happen during a prolonged hospital stay, following limb immobilization in a cast, or going into the weightlessness of outer space. Even a change in diet, such as eating only soft food due to the loss of teeth, will result in a noticeable decrease in the size and thickness of the jaw bones.<\/p>\r\n\r\n<h2 style=\"text-align: justify\"><strong><a id=\"12A1\"><\/a>Part 1: The Functions of the Skeletal System<\/strong><\/h2>\r\n<p style=\"text-align: justify\">Bone, or osseous tissue, is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body. In the areas of the skeleton where bones move (for example, the ribcage and joints), cartilage, a semi-rigid form of connective tissue, provides flexibility and smooth surfaces for movement. The skeletal system is the body system composed of bones and cartilage and performs the following critical functions for the human body:<\/p>\r\n\r\n<ul>\r\n \t<li>supports the body<\/li>\r\n \t<li>facilitates movement<\/li>\r\n \t<li>protects internal organs<\/li>\r\n \t<li>produces blood cells<\/li>\r\n \t<li>stores and releases minerals and fat<\/li>\r\n<\/ul>\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A1a\"><\/a>Support, Movement and Protection<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The most apparent functions of the skeletal system are the gross functions\u2014those visible by observation. Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body.<\/p>\r\n<p style=\"text-align: justify\">Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin.<\/p>\r\n<p style=\"text-align: justify\">Bones also facilitate movement by serving as points of attachment for your muscles. While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract. From a mechanical point of view, bones act as [pb_glossary id=\"2739\"]levers[\/pb_glossary] and [pb_glossary id=\"2740\"]joints[\/pb_glossary] serve as fulcrums (Figure 1). Unless a muscle spans a joint and contracts, a bone is not going to move.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"537\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image1-6.png\" alt=\"image\" width=\"537\" height=\"761\" \/> <strong>Figure 1. Bones Support Movement.<\/strong> Bones act as levers when muscles span a joint and contract. (credit: Benjamin J. DeLong)[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"621\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image2-6.png\" alt=\"image\" width=\"621\" height=\"804\" \/> <strong>Figure 2. Bones Protect the Brain.<\/strong> The cranium completely surrounds and protects the brain from non-traumatic injury.[\/caption]\r\n<p style=\"text-align: justify\">Bones also protect internal organs from injury by covering or surrounding them. For example, your ribs protect your lungs and heart, the bones of your vertebral column (spine) protect your spinal cord, and the bones of your cranium (skull) protect your brain (Figure 2).<\/p>\r\n<p style=\"text-align: justify\"><strong>Mineral Storage, Energy Storage, and Hematopoiesis:<\/strong> On a metabolic level, bone tissue performs several critical functions. For one, the bone matrix ([pb_glossary id=\"2298\"]ground substance[\/pb_glossary]) acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and phosphorus. These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes. Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses.<\/p>\r\n<p style=\"text-align: justify\">Bone also serves as a site for fat storage and blood cell production. The softer connective tissue that fills the interior of most bone is referred to as bone marrow (Figure 3). There are two types of bone marrow: yellow marrow and red marrow. [pb_glossary id=\"2742\"]Yellow marrow[\/pb_glossary] contains [pb_glossary id=\"2300\"]adipose[\/pb_glossary] tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of energy. [pb_glossary id=\"2741\"]Red marrow[\/pb_glossary] is where [pb_glossary id=\"2329\"]hematopoiesis[\/pb_glossary]\u2014the production of blood cells\u2014takes place. Red blood cells, white blood cells, and cell fragments called [pb_glossary id=\"2328\"]platelets[\/pb_glossary] are all produced in the red marrow.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"660\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image3-7.png\" alt=\"image\" width=\"660\" height=\"394\" \/> <strong>Figure 3. Head of the Femur Showing Red and Yellow Marrow.<\/strong> The head of the femur contains both yellow and red marrow. Yellow marrow stores fat. Red marrow is responsible for hematopoiesis. (credit: modification of work by \u201cstevenfruitsmaak\u201d\/Wikimedia Commons)[\/caption]\r\n<h2 style=\"text-align: justify\"><strong><a id=\"12A2\"><\/a>Part 2: Bone Classification<\/strong><\/h2>\r\n<p style=\"text-align: justify\">The 206 bones that compose the adult skeleton can be divided into five categories based on their shapes (Figure 4). Their shapes and their functions are related such that each categorical shape of bone has a distinct function.<\/p>\r\n<p style=\"text-align: justify\"><strong>Long Bones:<\/strong> A long bone is one that is cylindrical in shape, with a diameter smaller than its height. Keep in mind, however, that the term describes the shape of a bone, not its size. Long bones are found in the arms ([pb_glossary id=\"2746\"]humerus[\/pb_glossary], [pb_glossary id=\"2745\"]ulna[\/pb_glossary], and [pb_glossary id=\"2747\"]radius[\/pb_glossary]) and legs ([pb_glossary id=\"2379\"]femur[\/pb_glossary], [pb_glossary id=\"2748\"]tibia[\/pb_glossary], and [pb_glossary id=\"2749\"]fibula[\/pb_glossary]), as well as in the fingers ([pb_glossary id=\"2744\"]metacarpals[\/pb_glossary] and phalanges) and toes ([pb_glossary id=\"2743\"]metatarsals[\/pb_glossary] and [pb_glossary id=\"2750\"]phalanges[\/pb_glossary]). Long bones function as levers; they move when muscles contract.<\/p>\r\n<p style=\"text-align: justify\"><strong>Short Bones:<\/strong> A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness. The only short bones in the human skeleton are in the [pb_glossary id=\"2752\"]carpals[\/pb_glossary] of the wrists and the [pb_glossary id=\"2753\"]tarsals[\/pb_glossary] of the ankles. Short bones provide stability and support as well as some limited motion.<\/p>\r\n<p style=\"text-align: justify\"><strong>Flat Bones:<\/strong> The term \u201cflat bone\u201d is somewhat of a misnomer because, although a flat bone is typically thin, it is also often curved. Examples include the cranial bones of the skull, the [pb_glossary id=\"2755\"]scapulae[\/pb_glossary] (shoulder blades), the [pb_glossary id=\"2754\"]sternum[\/pb_glossary] (breastbone), and the ribs. Flat bones serve as points of attachment for muscles and often protect internal organs.<\/p>\r\n<p style=\"text-align: justify\"><strong>Irregular Bones:<\/strong> An irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification. These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Many facial bones, particularly the ones containing sinuses, are classified as irregular bones.<\/p>\r\n<p style=\"text-align: justify\"><strong>Sesamoid Bones:<\/strong> A sesamoid bone is a small, round bone that, as the name suggests, is shaped like a sesame seed. These bones form in tendons (the sheaths of tissue that connect bones to muscles) where a great deal of pressure is generated in a joint. The sesamoid bones protect [pb_glossary id=\"2736\"]tendons[\/pb_glossary] by helping them overcome compressive forces. Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and knees. The [pb_glossary id=\"2408\"]patellae[\/pb_glossary] (singular = patella) are the only sesamoid bones found in common with every person. Table 1 reviews bone classifications with their associated features, functions, and examples.<\/p>\r\n\r\n<table style=\"border-collapse: collapse;width: 100%\" border=\"0\"><caption>Table 1: Bone Classification by Shape<\/caption>\r\n<tbody>\r\n<tr>\r\n<th style=\"width: 25%\" scope=\"col\"><strong>Bone classification<\/strong><\/th>\r\n<th style=\"width: 25%\" scope=\"col\"><strong>Features<\/strong><\/th>\r\n<th style=\"width: 25%\" scope=\"col\"><strong>Function(s)<\/strong><\/th>\r\n<th style=\"width: 25%\" scope=\"col\"><strong>Examples<\/strong><\/th>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 25%\">Long<\/td>\r\n<td style=\"width: 25%\">Cylinder-like shape, longer than it is wide<\/td>\r\n<td style=\"width: 25%\">Leverage<\/td>\r\n<td style=\"width: 25%\">Femur, tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges<\/td>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 25%\">Short<\/td>\r\n<td style=\"width: 25%\">Cube-like shape, approximately equal in length, width, and thickness<\/td>\r\n<td style=\"width: 25%\">Provide stability &amp; support while allowing for some motion<\/td>\r\n<td style=\"width: 25%\">Carpals, tarsals<\/td>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 25%\">Flat<\/td>\r\n<td style=\"width: 25%\">Thin and curved<\/td>\r\n<td style=\"width: 25%\">Points of attachment for muscles; protectors of internal organs<\/td>\r\n<td style=\"width: 25%\">Sternum, ribs, scapulae, cranial bones<\/td>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 25%\">Irregular<\/td>\r\n<td style=\"width: 25%\">Complex shape<\/td>\r\n<td style=\"width: 25%\">Protect internal organs<\/td>\r\n<td style=\"width: 25%\">Vertebrae, facial bones<\/td>\r\n<\/tr>\r\n<tr>\r\n<td style=\"width: 25%\">Sesamoid<\/td>\r\n<td style=\"width: 25%\">Small and round; embedded in tendons<\/td>\r\n<td style=\"width: 25%\">Protect tendons from compressive forces<\/td>\r\n<td style=\"width: 25%\">Patellae<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<h2 style=\"text-align: justify\"><strong><a id=\"12A3\"><\/a>Part 3: Bone Structure<\/strong><\/h2>\r\n<p style=\"text-align: justify\">Bone tissue (osseous tissue) differs greatly from other tissues in the body. Bone is hard and many of its functions depend on that characteristic hardness. Later discussions in this chapter will show that bone is also dynamic in that its shape adjusts to accommodate stresses. This section will examine the gross anatomy of bone first and then move on to its histology.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A3a\"><\/a>Gross Anatomy of Bone<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The structure of a long bone allows for the best visualization of all of the parts of a bone (Figure 5). A long bone has two parts: the <strong>[pb_glossary id=\"2756\"]diaphysis[\/pb_glossary]<\/strong> and the <strong>[pb_glossary id=\"2757\"]epiphysis[\/pb_glossary]<\/strong>. The diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone. The hollow region in the diaphysis is called the <strong>[pb_glossary id=\"2758\"]medullary cavity[\/pb_glossary]<\/strong>, which is filled with [pb_glossary id=\"2742\"]yellow marrow[\/pb_glossary]. The walls of the diaphysis are composed of dense and hard <strong>[pb_glossary id=\"2759\"]compact bone[\/pb_glossary]<\/strong>. The wider section at each end of the bone is called the <strong>epiphysis<\/strong> (plural = epiphyses), which is filled with [pb_glossary id=\"2327\"]spongy bone[\/pb_glossary]. [pb_glossary id=\"2741\"]Red marrow[\/pb_glossary] fills the spaces in the spongy bone.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"903\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image5-6.png\" alt=\"image\" width=\"903\" height=\"1045\" \/> <strong>Figure 4. Classifications of Bones.<\/strong> Bones can be classified according to their shape.[\/caption]\r\n<p style=\"text-align: justify\">Each epiphysis meets the diaphysis at the metaphysis, the narrow area that contains the <strong>[pb_glossary id=\"2760\"]epiphyseal plate[\/pb_glossary]<\/strong> (growth plate), a layer of [pb_glossary id=\"2321\"]hyaline[\/pb_glossary] (transparent) cartilage in a growing bone. When the bone stops growing in early adulthood (approximately 18\u201321 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an [pb_glossary id=\"2761\"]epiphyseal line[\/pb_glossary].<\/p>\r\n<p style=\"text-align: justify\">The medullary cavity has a delicate membranous lining called the <strong>[pb_glossary id=\"2762\"]endosteum[\/pb_glossary] <\/strong>(end- = \u201cinside\u201d; oste- = \u201cbone\u201d), where bone growth, repair, and remodeling occur. The outer surface of the bone is covered with a fibrous membrane called the <strong>[pb_glossary id=\"2764\"]periosteum[\/pb_glossary] <\/strong>(peri\u2013 = \u201caround\u201d or \u201csurrounding\u201d). The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Tendons and ligaments also attach to bones at the periosteum. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints (Figure 6). In this region, the epiphyses are covered with <strong>[pb_glossary id=\"2763\"]articular cartilage[\/pb_glossary]<\/strong>, a thin layer of cartilage that reduces friction and acts as a shock absorber.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"619\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image6-6.png\" alt=\"image\" width=\"619\" height=\"1048\" \/> <strong>Figure 5. Anatomy of a Long Bone.<\/strong> A typical long bone shows the gross anatomical characteristics of bone.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1069\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image7-6.png\" alt=\"image\" width=\"1069\" height=\"535\" \/> <strong>Figure 6. Periosteum and Endosteum.<\/strong> The periosteum forms the outer surface of bone, and the endosteum lines the internal surfaces of bone, like the medullary cavity.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"811\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image8-7.png\" alt=\"image\" width=\"811\" height=\"409\" \/> <strong>Figure 7. Anatomy of a Flat Bone.<\/strong> This cross-section of a flat bone shows the spongy bone (diplo\u00eb) lined on either side by a layer of compact bone.[\/caption]\r\n<p style=\"text-align: justify\">Flat bones, like those of the cranium, consist of a layer of <strong>[pb_glossary id=\"2765\"]diplo\u00eb[\/pb_glossary]<\/strong> (spongy bone), lined on either side by a layer of compact bone (Figure 7). The two layers of compact bone and the interior spongy bone work together to protect the internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A3b\"><\/a>Bone Cells and Tissue<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Bone contains a relatively small number of cells entrenched in a matrix of [pb_glossary id=\"2174\"]collagen[\/pb_glossary] fibres that provide a surface for inorganic salt crystals to adhere. These salt crystals, made of a substance called [pb_glossary id=\"2324\"]hydroxyapatite[\/pb_glossary], form when calcium phosphate and calcium carbonate combine with other inorganic salts and solidify, (i.e. calcify) on the collagen fibres. The crystals give bones their hardness and strength, while the collagen fibres give them flexibility so that they are not brittle.<\/p>\r\n<p style=\"text-align: justify\">Although bone cells compose a small amount of the bone volume, they are crucial to the function of bones. Four types of cells are found within bone tissue: osteoblasts, osteocytes, osteogenic cells, and osteoclasts (Figure 8).<\/p>\r\n<p style=\"text-align: justify\">The <strong>[pb_glossary id=\"2766\"]osteoblast[\/pb_glossary]<\/strong> is the bone cell responsible for forming new bone and is found in the growing portions of bone, including the periosteum and endosteum. Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and calcium salts. As the secreted matrix surrounding the osteoblast calcifies, the osteoblast become trapped within it; as a result, it changes in structure and becomes an <strong>[pb_glossary id=\"2325\"]osteocyte[\/pb_glossary]<\/strong>, the primary cell of mature bone and the most common type of bone cell. Each osteocyte is located in a space called a<strong> [pb_glossary id=\"2318\"]lacuna[\/pb_glossary]<\/strong> and is surrounded by bone matrix. Osteocytes maintain the mineral concentration of the matrix. Like osteoblasts, osteocytes lack mitotic activity. They can communicate with each other and receive nutrients via long cytoplasmic processes that extend through <strong>[pb_glossary id=\"2767\"]canaliculi[\/pb_glossary]<\/strong> (singular = canaliculus), channels within the bone matrix.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"807\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image9-6.png\" alt=\"image\" width=\"807\" height=\"564\" \/> <strong>Figure 8. Bone Cells.<\/strong> Four types of cells are found within bone tissue. Osteogenic cells are undifferentiated and develop into osteoblasts. When osteoblasts get trapped within the calcified matrix, their structure and function changes, and they become osteocytes. Osteoclasts develop from monocytes and macrophages and differ in appearance from other bone cells.[\/caption]\r\n\r\nIf osteoblasts and osteocytes are incapable of [pb_glossary id=\"2709\"]mitosis[\/pb_glossary], then how are they replenished when old ones die? The answer lies in the properties of a third category of bone cells\u2014the <strong>[pb_glossary id=\"2770\"]osteogenic cell[\/pb_glossary]<\/strong>. These osteogenic cells are undifferentiated with high mitotic activity and they are the only bone cells that divide. Immature osteogenic cells are found in the deep layers of the periosteum and the marrow. They differentiate and develop into osteoblasts.\r\n<p style=\"text-align: justify\">The dynamic nature of bone means that new tissue is constantly formed, and old, injured, or unnecessary bone is dissolved for repair or for calcium release. The cell responsible for bone resorption, or breakdown, is the <strong>[pb_glossary id=\"2768\"]osteoclast[\/pb_glossary]<\/strong>. They are found on bone surfaces, are multinucleated, and originate from [pb_glossary id=\"2769\"]monocytes[\/pb_glossary] and [pb_glossary id=\"2307\"]macrophages[\/pb_glossary], two types of white blood cells, not from osteogenic cells. Osteoclasts are continually breaking down old bone while osteoblasts are continually forming new bone. The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone. Table 2 reviews the bone cells, their functions, and locations.<\/p>\r\n\r\n<table style=\"border-collapse: collapse;width: 100%;height: 70px\" border=\"0\"><caption>Table 2: Bone Cells<\/caption>\r\n<tbody>\r\n<tr style=\"height: 14px\">\r\n<th style=\"width: 18.9265%;height: 14px\" scope=\"col\"><strong>Cell type<\/strong><\/th>\r\n<th style=\"width: 33.1921%;height: 14px\" scope=\"col\"><strong>Function<\/strong><\/th>\r\n<th style=\"width: 47.8813%;height: 14px\" scope=\"col\"><strong>Location<\/strong><\/th>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 18.9265%;height: 14px\">Osteogenic cells<\/td>\r\n<td style=\"width: 33.1921%;height: 14px\">Develop into osteoblasts<\/td>\r\n<td style=\"width: 47.8813%;height: 14px\">Deep layers of the periosteum and the marrow<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 18.9265%;height: 14px\">Osteoblasts<\/td>\r\n<td style=\"width: 33.1921%;height: 14px\">Bone formation<\/td>\r\n<td style=\"width: 47.8813%;height: 14px\">Growing portions of bone, including periosteum and endosteum<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 18.9265%;height: 14px\">Osteocytes<\/td>\r\n<td style=\"width: 33.1921%;height: 14px\">Maintain mineral concentration of matrix<\/td>\r\n<td style=\"width: 47.8813%;height: 14px\">Entrapped in matrix (in lacunae)<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 18.9265%;height: 14px\">Osteoclasts<\/td>\r\n<td style=\"width: 33.1921%;height: 14px\">Bone resorption<\/td>\r\n<td style=\"width: 47.8813%;height: 14px\">Bone surfaces and at sites of old, injured, or unneeded bone<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<h5><strong><a id=\"12A3c\"><\/a>Compact and Spongy Bone<\/strong><\/h5>\r\nThe differences between compact and spongy bone are best explored via their histology. Most bones contain compact and spongy osseous tissue, but their distribution and concentration vary based on the bone\u2019s overall function. Compact bone is dense so that it can withstand compressive forces, while spongy (cancellous) bone has open spaces and supports shifts in weight distribution.\r\n<p style=\"text-align: justify\"><strong>1. Compact Bone:<\/strong> Compact bone is the denser, stronger of the two types of bone tissue (Figure 9). It can be found deep to the [pb_glossary id=\"2764\"]periosteum[\/pb_glossary] and in the [pb_glossary id=\"2756\"]diaphyses[\/pb_glossary] of long bones, where it provides support and protection.<\/p>\r\n<p style=\"text-align: justify\">The microscopic structural unit of compact bone is called an<strong> [pb_glossary id=\"2771\"]osteon[\/pb_glossary]<\/strong>, or Haversian system. Each osteon is composed of concentric rings of calcified matrix called [pb_glossary id=\"2774\"]lamellae[\/pb_glossary] (singular = lamella). Running down the center of each osteon is the <strong>[pb_glossary id=\"2772\"]central canal[\/pb_glossary]<\/strong>, or Haversian canal, which contains blood vessels, nerves, and lymphatic vessels. These vessels and nerves branch off at right angles through a <strong>[pb_glossary id=\"2773\"]perforating canal[\/pb_glossary]<\/strong>, also known as Volkmann\u2019s canals, to extend to the [pb_glossary id=\"2764\"]periosteum[\/pb_glossary] and [pb_glossary id=\"2762\"]endosteum[\/pb_glossary].<\/p>\r\n<p style=\"text-align: justify\">The [pb_glossary id=\"2325\"]osteocytes[\/pb_glossary] are located inside spaces called [pb_glossary id=\"2318\"]lacunae[\/pb_glossary] (singular = lacuna), found at the borders of adjacent [pb_glossary id=\"2774\"]lamellae[\/pb_glossary]. As described earlier, [pb_glossary id=\"2767\"]canaliculi[\/pb_glossary] connect with the canaliculi of other lacunae and eventually with the central canal. This system allows nutrients to be transported to the osteocytes and wastes to be removed from them.<\/p>\r\n<p style=\"text-align: justify\"><strong>2. Spongy (Cancellous) Bone:<\/strong> Like compact bone, <strong>[pb_glossary id=\"2327\"]spongy bone[\/pb_glossary],<\/strong> also known as cancellous bone, contains osteocytes housed in lacunae, but they are not arranged in concentric circles. Instead, the lacunae and osteocytes are found in a lattice-like network of matrix spikes called <strong>[pb_glossary id=\"2775\"]trabeculae[\/pb_glossary]<\/strong> (singular = trabecula) (Figure 10). The trabeculae may appear to be a random network, but each trabecula forms along lines of stress to provide strength to the bone. The spaces of the trabeculated network provide balance to the dense and heavy compact bone by making bones lighter so that muscles can move them more easily. In addition, the spaces in some spongy bones contain red marrow, protected by the trabeculae, where [pb_glossary id=\"2329\"]hematopoiesis[\/pb_glossary] occurs.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"889\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image11-6.png\" alt=\"image\" width=\"889\" height=\"1044\" \/> <strong>Figure 9. Compact Bone.<\/strong> (a) This cross-sectional view of compact bone shows the basic structural unit, the osteon. (b) In this micrograph of the osteon, you can clearly see the concentric lamellae and central canals. LM \u00d7 40. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1117\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image12-6.png\" alt=\"image\" width=\"1117\" height=\"739\" \/> <strong>Figure 10. Spongy Bone.<\/strong> Spongy bone is composed of trabeculae that contain the osteocytes. Red marrow fills the spaces in some bones.[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A3d\"><\/a>Blood and Nerve Supply<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The spongy bone and medullary cavity receive nourishment from arteries that pass through the compact bone. The arteries enter through the <strong>[pb_glossary id=\"2783\"]nutrient foramen[\/pb_glossary]<\/strong> (plural = foramina), a small opening in the diaphysis (Figure 11). The osteocytes in spongy bone are nourished by blood vessels of the [pb_glossary id=\"2764\"]periosteum[\/pb_glossary] that penetrate spongy bone and blood that circulates in the marrow cavities. As the blood passes through the marrow cavities, it is collected by veins, which then pass out of the bone through the foramen.<\/p>\r\n<p style=\"text-align: justify\">In addition to the blood vessels, nerves follow the same paths into the bone where they tend to concentrate in the more metabolically active regions of the bone. The nerves sense pain, and it appears the nerves also play roles in regulating blood supplies and in bone growth, hence their concentrations in metabolically active sites of the bone.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"579\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image13-6.png\" alt=\"image\" width=\"579\" height=\"807\" \/> <strong>Figure 11. Blood and Nerve Supply to Bone.<\/strong> Blood vessels and nerves enter the bone through the nutrient foramen.[\/caption]\r\n<h2 style=\"text-align: justify\"><strong><a id=\"12A4\"><\/a>Part 4: Bone Formation and Development<\/strong><\/h2>\r\n<p style=\"text-align: justify\">In the early stages of embryonic development, the embryo\u2019s skeleton consists of fibrous membranes and [pb_glossary id=\"2321\"]hyaline cartilage[\/pb_glossary]. By the sixth or seventh week of embryonic life, the actual process of bone development, <strong>[pb_glossary id=\"2784\"]ossification[\/pb_glossary]<\/strong> (osteogenesis), begins. There are two osteogenic pathways\u2014[pb_glossary id=\"2785\"]intramembranous ossification[\/pb_glossary] and [pb_glossary id=\"2792\"]endochondral ossification[\/pb_glossary]\u2014but bone is the same regardless of the pathway that produces it.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4a\"><\/a>Cartilage Templates<\/strong><\/h5>\r\n<p style=\"text-align: justify\">Bone is a replacement tissue; that is, it uses a model tissue on which to lay down its mineral matrix. For skeletal development, the most common template is cartilage. During fetal development, a framework is laid down that determines where bones will form. This framework is a flexible, semi-solid cartilage matrix produced by chondroblasts. As the matrix surrounds and isolates [pb_glossary id=\"2788\"]chondroblasts[\/pb_glossary], they mature into cells called chondrocytes. Unlike most connective tissues, cartilage is [pb_glossary id=\"2286\"]avascular[\/pb_glossary], meaning that it has no blood vessels supplying nutrients and removing metabolic wastes. All of these functions are carried on by diffusion through the matrix. This is why damaged cartilage does not repair itself as readily as most tissues do.<\/p>\r\n<p style=\"text-align: justify\">Throughout fetal development and into childhood growth and development, bone forms on the cartilaginous matrix. By the time a fetus is born, most of the cartilage has been replaced with bone. Some additional cartilage will be replaced throughout childhood, and some cartilage remains in the adult skeleton.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4b\"><\/a>Intramembranous Ossification<\/strong><\/h5>\r\n<p style=\"text-align: justify\">During <strong>[pb_glossary id=\"2785\"]intramembranous ossification[\/pb_glossary]<\/strong>, compact and spongy bone develops directly from sheets of [pb_glossary id=\"2306\"]mesenchymal[\/pb_glossary] (undifferentiated) connective tissue. The flat bones of the face, most of the cranial bones, and the [pb_glossary id=\"2786\"]clavicles[\/pb_glossary] (collarbones) are initially formed via intramembranous ossification.<\/p>\r\n<p style=\"text-align: justify\">The process begins when mesenchymal cells in the embryonic skeleton gather together and begin to differentiate into specialized cells (Figure 12a). Some of these cells will form capillaries, while others will become osteogenic cells and then osteoblasts. Although they will ultimately be spread out by the formation of bone tissue, early osteoblasts appear in a cluster called an <strong>[pb_glossary id=\"2789\"]ossification centre[\/pb_glossary]<\/strong>.<\/p>\r\n<p style=\"text-align: justify\">The osteoblasts secrete <strong>[pb_glossary id=\"2790\"]osteoid[\/pb_glossary]<\/strong>, uncalcified matrix, which calcifies (hardens) within a few days as mineral salts are deposited on it, thereby entrapping the osteoblasts within. Once entrapped, the osteoblasts become osteocytes (Figure 12b). As osteoblasts transform into osteocytes, [pb_glossary id=\"2770\"]osteogenic cells[\/pb_glossary] in the surrounding connective tissue differentiate into new [pb_glossary id=\"2766\"]osteoblasts[\/pb_glossary].<\/p>\r\n<p style=\"text-align: justify\">Osteoid (unmineralized bone matrix) secreted around the capillaries results in a [pb_glossary id=\"2775\"]trabecular[\/pb_glossary] matrix, while osteoblasts on the surface of the spongy bone become the periosteum (Figure 12c). The periosteum then creates a protective layer of compact bone superficial to the trabecular bone. The trabecular bone crowds nearby blood vessels, which eventually condense into [pb_glossary id=\"2741\"]red marrow[\/pb_glossary] (Figure 12d).<\/p>\r\n<p style=\"text-align: justify\">Intramembranous ossification begins <em>in utero <\/em>during fetal development and continues on into adolescence. At birth, the skeleton is not fully ossified. Most joints of the skull, for example, are more mobile in an infant than an adult to allow the skull to deform during passage through the birth canal. The flat bones of the cranium continue to grow throughout childhood, ultimately being separated by narrow immobile joints called sutures.\u00a0 Each clavicle also initially (at about 6 weeks of embryonic age) forms by [pb_glossary id=\"2785\"]intramembranous ossification[\/pb_glossary] from two [pb_glossary id=\"2791\"]primary ossification centres[\/pb_glossary] that fuse together <em>in utero<\/em> to form a single bone with cartilage at both ends.\u00a0 This cartilage later ossifies to form the mature clavicles with [pb_glossary id=\"2763\"]articular cartilage[\/pb_glossary] on either end (usually in an individual\u2019s early twenties).\u00a0 The last bones to ossify via intramembranous ossification are the flat bones of the face, which reach their adult size at the end of the adolescent growth spurt.\u00a0 The mandible in an infant, for example, consists of two separate bones (left and right), connected by a joint called a [pb_glossary id=\"2977\"]symphysis[\/pb_glossary].\u00a0 This mandibular symphysis is fully ossified within the first year of life, permanently fusing the left and right bones to form the mandible.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1210\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image14-6.png\" alt=\"image\" width=\"1210\" height=\"844\" \/> <strong>Figure 12. Intramembranous Ossification.<\/strong> Intramembranous ossification follows four steps. (a) Mesenchymal cells group into clusters, and ossification centers form. (b) Secreted osteoid traps osteoblasts, which then become osteocytes. (c) Trabecular matrix and periosteum form. (d) Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red marrow.[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4c\"><\/a>Endochondral Ossification<\/strong><\/h5>\r\n<p style=\"text-align: justify\">In <strong>[pb_glossary id=\"2792\"]endochondral ossification[\/pb_glossary]<\/strong>, bone develops by replacing hyaline cartilage. Cartilage does not become bone, but instead serves as a template to be completely replaced by new bone. Endochondral ossification takes much longer than [pb_glossary id=\"2785\"]intramembranous ossification[\/pb_glossary]. Bones at the base of the skull and long bones form via endochondral ossification.<\/p>\r\n<p style=\"text-align: justify\">In a long bone, for example, at about 6 to 8 weeks after conception, some of the [pb_glossary id=\"2306\"]mesenchymal[\/pb_glossary] cells differentiate into chondroblasts (cells that secrete the organic components of cartilage matrix) that form the cartilaginous skeletal precursor of the bones (Figure 13a). Soon after, the <strong>[pb_glossary id=\"2319\"]perichondrium[\/pb_glossary]<\/strong>, a membrane that covers the cartilage, appears (Figure 13b).<\/p>\r\n<p style=\"text-align: justify\">As more matrix is produced, the [pb_glossary id=\"2320\"]chondrocyte[\/pb_glossary] in the center of the cartilaginous model grow in size. As the matrix calcifies, nutrients can no longer reach the chondrocytes. This results in their death and the disintegration of the surrounding cartilage. Blood vessels invade the resulting spaces, not only enlarging the cavities but also carrying [pb_glossary id=\"2770\"]osteogenic cells[\/pb_glossary] with them, many of which will become [pb_glossary id=\"2766\"]osteoblasts[\/pb_glossary] (Figure 13c). These enlarging spaces eventually combine to become the [pb_glossary id=\"2758\"]medullary cavity[\/pb_glossary] (Figure 13d).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"782\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image15-6.png\" alt=\"image\" width=\"782\" height=\"1041\" \/> <strong>Figure 13. Endochondral Ossification.<\/strong> Endochondral ossification follows five steps. (a) Mesenchymal cells differentiate into chondroblasts that secrete cartilage matrix to form a hyaline cartilage model of the future bony skeleton.\u00a0 The perichondrium forms. (b) The cartilage model starts to calcify; chondrocytes begin to die and the cartilage begins to degenerate. (c) Periosteal bud penetrates cartilage of the diaphysis; the primary ossification center develops.\u00a0 A bony collar develops around the diaphysis of the bone.\u00a0 Perichondrium transforms into periosteum.\u00a0 (d) Cartilage continue to grow at ends of the bone. Medullary cavity forms. (e) Periosteal buds penetrate cartilage at epiphyses; secondary ossification centers develop. (f) Cartilage remains at epiphyseal (growth) plate and at joint surface as articular cartilage.[\/caption]\r\n<p style=\"text-align: justify\">As the cartilage grows, capillaries penetrate it. This penetration initiates the transformation of the [pb_glossary id=\"2319\"]perichondrium[\/pb_glossary] into the bone-producing periosteum. Here, the osteoblasts form a periosteal collar of compact bone around the cartilage of the [pb_glossary id=\"2756\"]diaphysis[\/pb_glossary]. By the second or third month of fetal life, bone cell development and ossification ramps up and creates the <strong>[pb_glossary id=\"2791\"]primary ossification centre[\/pb_glossary]<\/strong>, a region deep in the periosteal collar where ossification begins (Figure 13c).<\/p>\r\n<p style=\"text-align: justify\">While these deep changes are occurring, chondrocytes and cartilage continue to grow at the ends of the bone (the future [pb_glossary id=\"2757\"]epiphyses[\/pb_glossary]), which increases the bone\u2019s length at the same time bone is replacing cartilage in the diaphyses. By the time the fetal skeleton is fully formed, cartilage only remains at the joint surface as articular cartilage and between the diaphysis and epiphysis as the [pb_glossary id=\"2760\"]epiphyseal plate[\/pb_glossary], the latter of which is responsible for the longitudinal growth of bones (Figure 13f). After birth, this same sequence of events (matrix mineralization, death of chondrocytes, invasion of blood vessels from the [pb_glossary id=\"2764\"]periosteum[\/pb_glossary], and seeding with osteogenic cells that become osteoblasts) occurs in the epiphyseal regions, and each of these centers of activity is referred to as a <strong>[pb_glossary id=\"2793\"]secondary ossification centre[\/pb_glossary]<\/strong>\u00a0(Figure 13e).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"672\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image16-7.png\" alt=\"image\" width=\"672\" height=\"1045\" \/> <strong>Figure 14. Bone Growth in Length.<\/strong> The epiphyseal plate is responsible for longitudinal bone growth.[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4d\"><\/a>How Bones Grow in Length<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The [pb_glossary id=\"2760\"]epiphyseal plate[\/pb_glossary] is the area of growth in a long bone. It is a layer of [pb_glossary id=\"2321\"]hyaline cartilage[\/pb_glossary] where ossification occurs in immature bones. On the epiphyseal side of the epiphyseal plate, cartilage is formed. On the diaphyseal side, cartilage is ossified, and the [pb_glossary id=\"2756\"]diaphysis[\/pb_glossary] grows in length. The epiphyseal plate is composed of four zones of cells and activity (Figure 14). The <strong>[pb_glossary id=\"2807\"]reserve zone[\/pb_glossary]<\/strong> is the region closest to the epiphyseal end of the plate and contains small chondrocytes within the matrix. These chondrocytes do not participate in bone growth but secure the epiphyseal plate to the osseous tissue of the epiphysis.<\/p>\r\n<p style=\"text-align: justify\">The <strong>[pb_glossary id=\"2808\"]proliferative zone[\/pb_glossary]<\/strong> is the next layer toward the diaphysis and contains stacks of slightly larger [pb_glossary id=\"2320\"]chondrocytes[\/pb_glossary]. It makes new chondrocytes (via mitosis) to replace those that die at the diaphyseal end of the plate. Chondrocytes in the next layer, the <strong>[pb_glossary id=\"2809\"]zone of maturation and hypertrophy[\/pb_glossary]<\/strong>, are older and larger than those in the proliferative zone. The more mature cells are situated closer to the diaphyseal end of the plate. The longitudinal growth of bone is a result of cellular division in the proliferative zone and the maturation of cells in the zone of maturation and hypertrophy.<\/p>\r\n<p style=\"text-align: justify\">Most of the chondrocytes in <strong>the [pb_glossary id=\"2810\"]zone of calcified matrix[\/pb_glossary]<\/strong>, the zone closest to the diaphysis, are dead because the [pb_glossary id=\"2297\"]matrix[\/pb_glossary] around them has calcified. Capillaries and [pb_glossary id=\"2766\"]osteoblasts[\/pb_glossary] from the diaphysis penetrate this zone, and the osteoblasts secrete bone tissue on the remaining calcified cartilage.<\/p>\r\n<p style=\"text-align: justify\">Thus, the zone of calcified matrix connects the epiphyseal plate to the diaphysis. A bone grows in length when osseous tissue is added to the diaphysis.<\/p>\r\n<p style=\"text-align: justify\">Bones continue to grow in length until early adulthood. The rate of growth is controlled by hormones, which will be discussed later. When the chondrocytes in the epiphyseal plate cease their proliferation and bone replaces the cartilage, longitudinal growth stops. All that remains of the epiphyseal plate is the now fully ossified epiphyseal line (Figure 15).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"787\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image17-5.png\" alt=\"image\" width=\"787\" height=\"624\" \/> <strong>Figure 15. Progression from Epiphyseal Plate to Epiphyseal Line.<\/strong> As a bone matures, the epiphyseal plate fully ossifies into an epiphyseal line. (a) Epiphyseal plates are visible in a growing bone. (b) Epiphyseal lines are the remnants of epiphyseal plates in a mature bone.[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"#12A4e\"><\/a>How Bones Grow in Diameter<\/strong><\/h5>\r\n<p style=\"text-align: justify\">While bones are increasing in length, they are also increasing in diameter; growth in diameter can continue even after longitudinal growth ceases. This is called appositional growth. Osteoclasts resorb old bone that lines the medullary cavity, while osteoblasts, via intramembranous ossification, produce new bone tissue beneath the periosteum. The erosion of old bone along the medullary cavity and the deposition of new bone beneath the periosteum not only increase the diameter of the diaphysis but also increase the diameter of the medullary cavity. This process is called <strong>modeling<\/strong>.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4f\"><\/a>Bone Remodeling<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The process in which matrix is resorbed on one surface of a bone and deposited on another is known as bone modeling. Modeling primarily takes place during a bone\u2019s growth. However, in adult life, bone undergoes <strong>remodeling<\/strong>, in which resorption of old or damaged bone takes place on the same surface where osteoblasts lay new bone to replace that which is resorbed. Injury, exercise, and other activities lead to remodeling. Those influences are discussed later in the unit, but even without injury or exercise, about 5 to 10 percent of the skeleton is remodeled annually just by destroying old bone and renewing it with fresh bone.<\/p>\r\n\r\n<h2 style=\"text-align: justify\"><strong><a id=\"12A5\"><\/a>Part 5: Fractures<\/strong><\/h2>\r\n<p style=\"text-align: justify\">A <strong>fracture<\/strong> is a broken bone. It will heal whether or not a physician resets it in its anatomical position. If the bone is not reset correctly, the healing process will keep the bone in its deformed position. Please note that the material in this section (fractures) is not part of the course objectives and therefore not examinable.<\/p>\r\n<p style=\"text-align: justify\"><strong>Types of Fractures: <\/strong>Fractures are classified by their complexity, location, and other features (Figure 16). Table 3 outlines common types of fractures. Some fractures may be described using more than one term because it may have the features of more than one type (e.g., an open transverse fracture). Of the types pictured in Figure 16 and Table 3, you are only required to understand the details of closed, open, comminuted, and greenstick fractures.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"551\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image18-5.png\" alt=\"image\" width=\"551\" height=\"1048\" \/> <strong>Figure 16. Types of Fractures.<\/strong> Compare healthy bone with different types of fractures:(a) closed fracture, (b) open fracture, (c) transverse fracture, (d) spiral fracture, (e) comminuted fracture, (f) impacted fracture, (g) greenstick fracture, and (h) oblique fracture.[\/caption]\r\n<table style=\"border-collapse: collapse;width: 100%;height: 141px\" border=\"0\"><caption>Table 3: Types of Fractures<\/caption>\r\n<tbody>\r\n<tr style=\"height: 14px\">\r\n<th style=\"width: 21.4689%;height: 14px\" scope=\"col\"><strong>Type of fracture<\/strong><\/th>\r\n<th style=\"width: 78.5311%;height: 14px\" scope=\"col\"><strong>Description<\/strong><\/th>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 21.4689%;height: 14px\">Transverse<\/td>\r\n<td style=\"width: 78.5311%;height: 14px\">Occurs straight across the long axis of the bone<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 21.4689%;height: 14px\">Oblique<\/td>\r\n<td style=\"width: 78.5311%;height: 14px\">Occurs at an angle that is not 90 degrees<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 21.4689%;height: 14px\">Spiral<\/td>\r\n<td style=\"width: 78.5311%;height: 14px\">Bone segments are pulled apart as a result of a twisting motion<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 21.4689%;height: 14px\">Comminuted<\/td>\r\n<td style=\"width: 78.5311%;height: 14px\">Several breaks result in many small pieces between two large segments<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 21.4689%;height: 14px\">Impacted<\/td>\r\n<td style=\"width: 78.5311%;height: 14px\">One fragment is driven into the other (usually a result of compression)<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 21.4689%;height: 14px\">Greenstick<\/td>\r\n<td style=\"width: 78.5311%;height: 14px\">A partial fracture in which only one side of the bone is broken<\/td>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<td style=\"width: 21.4689%;height: 29px\">Open (compound)<\/td>\r\n<td style=\"width: 78.5311%;height: 29px\">A fracture in which at least one end of the broken bone tears through the skin; carries a high risk of infection<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 21.4689%;height: 14px\">Closed (simple)<\/td>\r\n<td style=\"width: 78.5311%;height: 14px\">A fracture in which the skin remains intact<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<h1 style=\"text-align: justify\"><b>B. Divisions of the Skeletal System<\/b><\/h1>\r\n<p style=\"text-align: justify\"><span style=\"font-size: 1em\">The skeletal system includes all of the bones, cartilages, and ligaments of the body that support and give shape to the body and body structures. The <\/span><strong style=\"font-size: 1em\">skeleton<\/strong><span style=\"font-size: 1em\"> consists of the bones of the body. For adults, there are 206 bones in the skeleton. Younger individuals have higher numbers of bones because some bones fuse together during childhood and adolescence to form an adult bone.\u00a0 <\/span>The skeleton is subdivided into two major divisions - the axial skeleton and the appendicular skeleton.<\/p>\r\n<p style=\"text-align: justify\"><strong>The Axial Skeleton:<\/strong> The skeleton is subdivided into two major divisions\u2014the axial skeleton and appendicular skeleton. The <strong>[pb_glossary id=\"2812\"]axial skeleton[\/pb_glossary]<\/strong> forms the vertical, central axis of the body and includes all bones of the head, neck, chest, and back (Figure 17). It serves to protect the brain, spinal cord, heart, and lungs. It also serves as the attachment site for muscles that move the head, neck, and back, and for muscles that act across the shoulder and hip joints to move their corresponding limbs.<\/p>\r\n<p style=\"text-align: justify\">The axial skeleton of the adult consists of 80 bones, including the <strong>skull<\/strong>, the <strong>[pb_glossary id=\"2815\"]vertebral column[\/pb_glossary]<\/strong>, and the <strong>[pb_glossary id=\"2816\"]thoracic cage[\/pb_glossary]<\/strong>. The skull is formed by 22 bones. Also associated with the head are an additional seven bones, including the <strong>[pb_glossary id=\"2813\"]hyoid bone[\/pb_glossary]<\/strong> and the <strong>ear [pb_glossary id=\"2611\"]ossicles[\/pb_glossary]<\/strong>\u00a0(three small bones found in each middle ear). The vertebral column consists of 24 bones, each called a <strong>[pb_glossary id=\"2818\"]vertebra[\/pb_glossary]<\/strong>, plus the <strong>[pb_glossary id=\"2817\"]sacrum[\/pb_glossary]<\/strong> and <strong>[pb_glossary id=\"2409\"]coccyx[\/pb_glossary]<\/strong>. The thoracic cage includes the 12 pairs of <strong>ribs<\/strong>, and the <strong>[pb_glossary id=\"2754\"]sternum[\/pb_glossary]<\/strong>, the flattened bone of the [pb_glossary id=\"2357\"]anterior[\/pb_glossary] chest.<\/p>\r\n<p style=\"text-align: justify\"><strong>The Appendicular Skeleton:<\/strong> The appendicular skeleton includes all bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton (Figure 17). There are 126 bones in the appendicular skeleton of an adult. The bones of the appendicular skeleton are covered later in the unit.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1028\"]<img style=\"color: #373d3f;font-weight: bold;font-size: 1em\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image20-5.png\" alt=\"image\" width=\"1028\" height=\"1043\" \/> <strong>Figure 17. Axial and Appendicular Skeleton.<\/strong> The axial skeleton supports the head, neck, back, and chest and thus forms the vertical axis of the body. It consists of the skull, vertebral column (including the sacrum and coccyx), and the thoracic cage, formed by the ribs and sternum. The appendicular skeleton is made up of all bones of the upper and lower limbs.[\/caption]\r\n<h2><strong><a id=\"12B1\"><\/a>Part 1: The Axial Skeleton<\/strong><\/h2>\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12B1a\"><\/a>The Skull<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The <strong>cranium<\/strong> (skull) is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the <strong>[pb_glossary id=\"2819\"]facial bones[\/pb_glossary]<\/strong> and the <strong>brain case<\/strong>, or cranial vault (Figure 19). The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws. The rounded brain case surrounds and protects the brain and houses the middle and inner ear structures.<\/p>\r\n<p style=\"text-align: justify\">In the adult, the skull consists of 22 individual bones, 21 of which are immobile and united into a single unit. The 22nd bone is the <strong>[pb_glossary id=\"2820\"]mandible[\/pb_glossary]<\/strong> (lower jaw), which is the only moveable bone of the skull.<\/p>\r\n<p style=\"text-align: justify\"><strong>Development of the Skull:<\/strong> As the brain case bones grow in the fetal skull, they remain separated from each other by large areas of dense connective tissue, each of which is called a [pb_glossary id=\"2821\"]fontanelle[\/pb_glossary] (Figure 18). The fontanelles are the soft spots on an infant\u2019s head. They are important during birth because these areas allow the skull to change shape as it squeezes through the birth canal. After birth, the fontanelles allow for continued growth and expansion of the skull as the brain enlarges. The largest fontanelle is located on the anterior head, at the junction of the frontal and parietal bones. The fontanelles decrease in size and disappear by age 2. However, the skull bones remained separated from each other at the [pb_glossary id=\"2822\"]sutures[\/pb_glossary], which contain dense fibrous connective tissue that unites the adjacent bones. The connective tissue of the sutures allows for continued growth of the skull bones as the brain enlarges during childhood growth. This structure also means that, although the size of the cranium increases from birth to adulthood, proportionately it does so less than other parts of the skeleton; the relative size of the cranium in proportion to the rest of the body therefore decreases with age from birth to adulthood.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1671\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image21-5.png\" alt=\"image\" width=\"1671\" height=\"557\" \/> <strong>Figure 18. Newborn Skull.<\/strong> The bones of the newborn skull are not fully ossified and are separated by large areas called fontanelles, which are filled with fibrous connective tissue. The fontanelles allow for continued growth of the skull after birth. At the time of birth, the facial bones are small and underdeveloped, and the mastoid process has not yet formed.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1256\"]<img style=\"color: #373d3f;font-weight: bold;font-size: 1em\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image22-5.png\" alt=\"image\" width=\"1256\" height=\"1036\" \/> <strong>Figure 19. Parts of the Skull.<\/strong> The skull consists of the rounded brain case that houses the brain and the facial bones that form the upper and lower jaws, nose, orbits, and other facial structures.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1234\"]<img style=\"color: #373d3f;font-weight: bold;font-size: 1em\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image23-4.png\" alt=\"image\" width=\"1234\" height=\"1041\" \/> <strong>Figure 20. Anterior View of Skull.<\/strong> An anterior view of the skull shows the bones that form the forehead, orbits (eye sockets), nasal cavity, nasal septum, and upper and lower jaws.[\/caption]\r\n<p style=\"text-align: justify\"><strong>Bones of the Brain Case:<\/strong> The brain case contains and protects the brain (Figure 19). The interior space that is almost completely occupied by the brain is called the <strong>[pb_glossary id=\"2391\"]cranial cavity[\/pb_glossary]<\/strong>.<\/p>\r\n<p style=\"text-align: justify\">The brain case consists of eight bones (Figures 20 &amp; 21). These include the paired [pb_glossary id=\"2823\"]parietal[\/pb_glossary] and [pb_glossary id=\"2824\"]temporal[\/pb_glossary] bones, plus the unpaired [pb_glossary id=\"2825\"]frontal[\/pb_glossary], [pb_glossary id=\"2826\"]occipital[\/pb_glossary], [pb_glossary id=\"2827\"]sphenoid[\/pb_glossary], and [pb_glossary id=\"2828\"]ethmoid[\/pb_glossary] bones. For our purposes, we will not be specifying the details of the sphenoid and ethmoid bones.<\/p>\r\n<p style=\"text-align: justify\">1. Parietal Bone: The <strong>[pb_glossary id=\"2823\"]parietal bone[\/pb_glossary]<\/strong> forms most of the upper lateral side of the skull (Figures 21 &amp; 22). These are paired bones, with the right and left parietal bones joining together at the top of the skull. Each parietal bone is also bounded anteriorly by the frontal bone, inferiorly by the temporal bone, and posteriorly by the occipital bone.<\/p>\r\n<p style=\"text-align: justify\">2. Temporal Bone: The <strong>[pb_glossary id=\"2620\"]temporal bone[\/pb_glossary]<\/strong> forms the lower lateral side of the skull (Figure 21). Common wisdom has it that the temporal bone (temporal = \u201ctime\u201d) is so named because this area of the head (the temple) is where hair typically first turns gray, indicating the passage of time.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1514\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image24-4.png\" alt=\"image\" width=\"1514\" height=\"1037\" \/> <strong>Figure 21. Lateral View of Skull.<\/strong> The lateral skull shows the large rounded brain case, zygomatic arch, and the upper and lower jaws. The zygomatic arch is formed jointly by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. The shallow space above the zygomatic arch is the temporal fossa. The space inferior to the zygomatic arch and deep to the posterior mandible is the infratemporal fossa.[\/caption]\r\n<p style=\"text-align: justify\">3. Frontal Bone: The [pb_glossary id=\"2825\"]frontal bone[\/pb_glossary] is the single bone that forms the forehead (Figure 20).<\/p>\r\n<p style=\"text-align: justify\">4. Occipital Bone: The <strong>[pb_glossary id=\"2826\"]occipital bone[\/pb_glossary]<\/strong> is the single bone that forms the posterior skull and posterior base of the cranial cavity (Figures 21 &amp; 22). On its outside surface, at the posterior midline, is a small protrusion called the <strong>external occipital protuberance<\/strong>, which serves as an attachment site for a ligament of the posterior neck.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"809\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image25-4.png\" alt=\"image\" width=\"809\" height=\"628\" \/> <strong>Figure 22. Posterior View of Skull.<\/strong> This view of the posterior skull shows attachment sites for muscles and joints that support the skull.[\/caption]\r\n<p style=\"text-align: justify\"><strong>Facial Bones of the Skull: <\/strong>The facial bones of the skull form the upper and lower jaws, the nose, nasal cavity and nasal septum, and the orbit. The facial bones include 14 bones, with six paired bones and two unpaired bones (Figures 20 &amp; 21). We will focus on the maxillary bones and the mandible bone.<\/p>\r\n<p style=\"text-align: justify\">1. Maxillary Bone: The <strong>[pb_glossary id=\"2832\"]maxillary bone[\/pb_glossary]<\/strong>, often referred to simply as the maxilla (plural = maxillae), is one of a pair that together form the upper jaw, much of the hard palate, the medial floor of the orbit, and the lateral base of the nose (Figures 20 &amp; 21).<\/p>\r\n<p style=\"text-align: justify\">2. Mandible: The <strong>[pb_glossary id=\"2820\"]mandible[\/pb_glossary]<\/strong> forms the lower jaw and is the only moveable bone of the skull. At the time of birth, the mandible consists of paired right and left bones, but these fuse together during the first year to form the single U-shaped mandible of the adult skull (Figures 20 &amp; 21).<\/p>\r\n<p style=\"text-align: justify\"><strong>The Bones of the Middle Ear:<\/strong> Three small bones ([pb_glossary id=\"2611\"]ossicles[\/pb_glossary]) are found on either side of the head in the middle ear. These are the malleus, incus, and stapes, and they function in transferring the vibrations from the eardrum (tympanic membrane) to the inner ear.<\/p>\r\n<p style=\"text-align: justify\"><strong>The Hyoid Bone:<\/strong> The [pb_glossary id=\"2813\"]hyoid bone[\/pb_glossary] is an independent bone that does not contact any other bone and thus is not part of the skull (Figure 23). It is a small U-shaped bone located in the upper neck near the level of the inferior mandible, with the tips of the \u201cU\u201d pointing posteriorly. The hyoid serves as the base for the tongue above and is attached to the larynx below and the pharynx posteriorly. The hyoid is held in position by a series of small muscles that attach to it either from above or below. These muscles act to move the hyoid up\/down or forward\/back. Movements of the hyoid are coordinated with movements of the tongue, larynx, and pharynx during swallowing and speaking.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12B1b\"><\/a>The Vertebral Column<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The vertebral column is also known as the spinal column or spine (Figure 24). It consists of a sequence of vertebrae (singular = vertebra), each of which is separated and united by an <strong>intervertebral disc<\/strong>. Together, the vertebrae and intervertebral discs form the vertebral column. It is a flexible column that supports the head, neck, and body and allows for their movements. It also protects the spinal cord, which passes down the back through openings in the vertebra.<\/p>\r\n<p style=\"text-align: justify\"><strong>Regions of the Vertebral Column<\/strong>: The vertebral column originally develops as a series of 33 vertebrae, but this number is eventually reduced to 24 vertebrae, plus the sacrum and coccyx. The vertebral column is subdivided into five regions, with the vertebrae in each area named for that region and numbered in descending order. In the neck, there are seven cervical vertebrae, each designated with the letter \u201cC\u201d followed by its number. Superiorly, the C1 vertebra articulates (forms a joint) with the occipital condyles of the skull. Inferiorly, C1 articulates with the C2 vertebra, and so on. Below these are the 12 thoracic vertebrae, designated T1\u2013T12. The lower back contains the L1\u2013L5 lumbar vertebrae. The single sacrum, which is also part of the pelvis, is formed by the fusion of five sacral vertebrae. Similarly, the coccyx, or tailbone, results from the fusion of four small coccygeal vertebrae. However, the sacral and coccygeal fusions do not start until age 20 and are not completed until middle age.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"542\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image26-4.png\" alt=\"image\" width=\"542\" height=\"846\" \/> <strong>Figure 23. Hyoid Bone.<\/strong> The hyoid bone is located in the upper neck and does not join with any other bone. It provides attachments for muscles that act on the tongue, larynx, and pharynx.[\/caption]\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong>Curvatures of the Vertebral Column:<\/strong> The adult vertebral column does not form a straight line, but instead has four curvatures along its length (see Figure 24). These curves increase the vertebral column\u2019s strength, flexibility, and ability to absorb shock.<\/p>\r\n<p style=\"text-align: justify\">During fetal development, the body is flexed anteriorly into the fetal position, giving the entire vertebral column a single curvature that is concave anteriorly. In the adult, this fetal curvature is retained in two regions of the vertebral column as the <strong>thoracic curve<\/strong>, which involves the thoracic vertebrae, and the <strong>sacrococcygeal curve<\/strong>, formed by the sacrum and coccyx.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"817\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image27-4.png\" alt=\"image\" width=\"817\" height=\"779\" \/> <strong>Figure 24. Vertebral Column.<\/strong> The adult vertebral column consists of 24 vertebrae, plus the sacrum and coccyx. The vertebrae are divided into three regions: cervical C1\u2013C7 vertebrae, thoracic T1\u2013T12 vertebrae, and lumbar L1\u2013L5 vertebrae. The vertebral column is curved, with two primary curvatures (thoracic and sacrococcygeal curves) and two secondary curvatures (cervical and lumbar curves).[\/caption]\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong>General Structure of a Vertebra:<\/strong> Within the different regions of the vertebral column, vertebrae vary in size and shape, but they all follow a similar structural pattern. A typical vertebra will consist of a body, a vertebral arch, and seven processes (Figure 25).<\/p>\r\n<p style=\"text-align: justify\">The <strong>[pb_glossary id=\"2843\"]body[\/pb_glossary]<\/strong> is the anterior portion of each vertebra and is the part that supports the body weight. Because of this, the vertebral bodies progressively increase in size and thickness going down the vertebral column. The bodies of adjacent vertebrae are separated and strongly united by an intervertebral disc.<\/p>\r\n<p style=\"text-align: justify\">The <strong>[pb_glossary id=\"2840\"]vertebral arch[\/pb_glossary]<\/strong> forms the posterior portion of each vertebra.<\/p>\r\n<p style=\"text-align: justify\">The large opening between the vertebral arch and body is the <strong>[pb_glossary id=\"2842\"]vertebral foramen[\/pb_glossary]<\/strong>, which contains the spinal cord. In the intact vertebral column, the vertebral foramina of all of the vertebrae align to form the <strong>[pb_glossary id=\"2841\"]vertebral (spinal) canal[\/pb_glossary]<\/strong>, which serves as the bony protection and passageway for the spinal cord down the back. When the vertebrae are aligned together in the vertebral column, notches in the margins of the pedicles of adjacent vertebrae together form an <strong>intervertebral foramen<\/strong>, the opening through which a spinal nerve exits from the vertebral column (Figure 26).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1091\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image28-4.png\" alt=\"image\" width=\"1091\" height=\"472\" \/> <strong>Figure 25. Parts of a Typical Vertebra.<\/strong> A typical vertebra consists of a body and a vertebral arch. The arch is formed by the paired pedicles and paired laminae. Arising from the vertebral arch are the transverse, spinous, superior articular, and inferior articular processes. The vertebral foramen provides for passage of the spinal cord. Each spinal nerve exits through an intervertebral foramen, located between adjacent vertebrae. Intervertebral discs unite the bodies of adjacent vertebra[\/caption]\r\n<p style=\"text-align: justify\">Seven processes arise from the vertebral arch. Each paired [pb_glossary id=\"2858\"]<strong>transverse process<\/strong>[\/pb_glossary] projects laterally and arises from the junction point between the pedicle and lamina. The single <strong>[pb_glossary id=\"2844\"]spinous process[\/pb_glossary]<\/strong> (vertebral spine) projects posteriorly at the midline of the back. The vertebral spines can easily be felt as a series of bumps just under the skin down the middle of the back. The transverse and spinous processes serve as important muscle attachment sites. A <strong>[pb_glossary id=\"2845\"]superior articular process[\/pb_glossary]<\/strong> extends or faces upward, and an <strong>[pb_glossary id=\"2846\"]inferior articular process[\/pb_glossary]<\/strong> faces or projects downward on each side of a vertebrae. The paired superior articular processes of one vertebra join with the corresponding paired inferior articular processes from the next higher vertebra. These junctions form slightly moveable joints between the adjacent vertebrae. The shape and orientation of the articular processes vary in different regions of the vertebral column and play a major role in determining the type and range of motion available in each region.<\/p>\r\n<p style=\"text-align: justify\"><strong>Regional Modifications of Vertebrae:<\/strong> In addition to the general characteristics of a typical vertebra described above, vertebrae also display characteristic size and structural features that vary between the different vertebral column regions. Thus, cervical vertebrae are smaller than lumbar vertebrae due to differences in the proportion of body weight that each will support. Thoracic vertebrae have sites for rib attachment, and the vertebrae that give rise to the sacrum and coccyx have fused together into single bones. We will focus on the anatomically distinct natures of the first two cervical vertebrae, the atlas and the axis.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"997\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image29-4.png\" alt=\"image\" width=\"997\" height=\"470\" \/> <strong>Figure 26. Intervertebral Disc.<\/strong> The bodies of adjacent vertebrae are separated and united by an intervertebral disc, which provides padding and allows for movements between adjacent vertebrae. The disc consists of a fibrous outer layer called the anulus fibrosus and a gel-like center called the nucleus pulposus. The intervertebral foramen is the opening formed between adjacent vertebrae for the exit of a spinal nerve.[\/caption]\r\n<p style=\"text-align: justify\"><strong>Cervical Vertebrae: <\/strong>Typical <strong>cervical vertebrae<\/strong>, such as C4 or C5, have several characteristic features that differentiate them from thoracic or lumbar vertebrae (Figure 27). Cervical vertebrae have a small body, reflecting the fact that they carry the least amount of body weight. Cervical vertebrae usually have a bifid (Y-shaped) [pb_glossary id=\"2844\"]spinous process[\/pb_glossary]. The [pb_glossary id=\"2858\"]transverse processes[\/pb_glossary] of the cervical vertebrae are sharply curved (U-shaped) to allow for passage of the cervical spinal nerves. Each transverse process also has an opening called the <strong>[pb_glossary id=\"2847\"]transverse foramen[\/pb_glossary]<\/strong>.<\/p>\r\n<p style=\"text-align: justify\">The first and second cervical vertebrae are further modified, giving each a distinctive appearance. The first cervical (C1) vertebra is also called the <strong>[pb_glossary id=\"2848\"]atlas[\/pb_glossary]<\/strong>, because this is the vertebra that supports the skull on top of the vertebral column (in Greek mythology, Atlas was the god who supported the heavens on his shoulders). The C1 vertebra does not have a body or spinous process. Instead, it is ring-shaped, consisting of an <strong>anterior arch<\/strong> and a <strong>posterior arch<\/strong>. The transverse processes of the atlas are longer and extend more laterally than do the transverse processes of any other cervical vertebrae. The superior articular processes face upward and are deeply curved for articulation with the occipital condyles on the base of the skull. The inferior articular processes are flat and face downward to join with the superior articular processes of the C2 vertebra.<\/p>\r\n<p style=\"text-align: justify\">The second cervical (C2) vertebra is called the <strong>[pb_glossary id=\"2849\"]axis[\/pb_glossary]<\/strong>, because it serves as the axis for rotation when turning the head toward the right or left. The axis resembles typical cervical vertebrae in most respects but is easily distinguished by the <strong>[pb_glossary id=\"2850\"]dens[\/pb_glossary]<\/strong> (odontoid process), a bony projection that extends upward from the vertebral body. The dens joins with the inner aspect of the anterior arch of the atlas, where it is held in place by transverse ligament.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"915\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image30-4.png\" alt=\"image\" width=\"915\" height=\"1045\" \/> <strong>Figure 27. Cervical Vertebrae.<\/strong> A typical cervical vertebra has a small body, a bifid spinous process, transverse processes that have a transverse foramen and are curved for spinal nerve passage. The atlas (C1 vertebra) does not have a body or spinous process. It consists of an anterior and a posterior arch and elongated transverse processes. The axis (C2 vertebra) has the upward projecting dens, which articulates with the anterior arch of the atlas.[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12B1c\"><\/a>The Thoracic Cage<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The [pb_glossary id=\"2816\"]thoracic cage[\/pb_glossary] (rib cage) forms the thorax (chest) portion of the body. It consists of the 12 pairs of ribs with their costal cartilages and the sternum (Figure 28). The ribs are anchored posteriorly to the 12 thoracic vertebrae (T1\u2013T12). The thoracic cage protects the heart and lungs.<\/p>\r\n<p style=\"text-align: justify\"><strong>Sternum: <\/strong>The [pb_glossary id=\"2754\"]sternum[\/pb_glossary] is the elongated bony structure that anchors the anterior thoracic cage. It consists of three parts: the [pb_glossary id=\"2851\"]manubrium[\/pb_glossary], body, and [pb_glossary id=\"2852\"]xiphoid process[\/pb_glossary].<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1144\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image31-4.png\" alt=\"image\" width=\"1144\" height=\"674\" \/> <strong>Figure 28. Thoracic Cage.<\/strong> The thoracic cage is formed by the (a) sternum and (b) 12 pairs of ribs with their costal cartilages. The ribs are anchored posteriorly to the 12 thoracic vertebrae. The sternum consists of the manubrium, body, and xiphoid process. The ribs are classified as true ribs (1\u20137) and false ribs (8\u201312). The last two pairs of false ribs are also known as floating ribs (11\u201312)[\/caption]\r\n<p style=\"text-align: justify\"><strong>Ribs: <\/strong>Each rib is a curved, flattened bone that contributes to the wall of the thorax. The ribs articulate posteriorly with the T1\u2013T12 thoracic vertebrae, and most attach anteriorly via their [pb_glossary id=\"2853\"]costal cartilages[\/pb_glossary] to the [pb_glossary id=\"2754\"]sternum[\/pb_glossary]. There are 12 pairs of ribs. The ribs are numbered 1\u201312 in accordance with the thoracic vertebrae.<\/p>\r\n<p style=\"text-align: justify\">The bony ribs do not extend anteriorly completely around to the sternum. Instead, each rib ends in a costal cartilage. These cartilages are made of hyaline cartilage and can extend for several inches. Most ribs are then attached, either directly or indirectly, to the sternum via their costal cartilage (Figure 28). The ribs are classified into three groups based on their relationship to the sternum.<\/p>\r\n<p style=\"text-align: justify\">Ribs 1\u20137 are classified as <strong>[pb_glossary id=\"2854\"]true ribs[\/pb_glossary]<\/strong> (vertebrosternal ribs). The costal cartilage from each of these ribs attaches directly to the sternum. Ribs 8\u201312 are called <strong>[pb_glossary id=\"2855\"]false ribs[\/pb_glossary]<\/strong> (vertebrochondral ribs). The costal cartilages from these ribs do not attach directly to the sternum. For ribs 8\u201310, the costal cartilages are attached to the cartilage of the next higher rib. Thus, the cartilage of rib 10 attaches to the cartilage of rib 9, rib 9 then attaches to rib 8, and rib 8 is attached to rib 7. The last two false ribs (11\u201312) are also called <strong>[pb_glossary id=\"2856\"]floating ribs[\/pb_glossary]<\/strong> (vertebral ribs). These are short ribs that do not attach to the sternum at all. Instead, their small costal cartilages terminate within the musculature of the lateral abdominal wall.<\/p>\r\n\r\n<h2 style=\"text-align: justify\"><strong><a id=\"12B2\"><\/a>Part 2. The Appendicular Skeleton<\/strong><\/h2>\r\n<p style=\"text-align: justify\">Attached to the axial skeleton are the limbs, whose 126 bones constitute the [pb_glossary id=\"2860\"]appendicular skeleton[\/pb_glossary] (Figure 29) These bones are divided into two groups: the bones that are located within the limbs themselves, and the [pb_glossary id=\"2859\"]girdle[\/pb_glossary] bones that attach the limbs to the axial skeleton. The bones of the shoulder region form the [pb_glossary id=\"2861\"]pectoral girdle[\/pb_glossary], which anchors the upper limb to the thoracic cage of the axial skeleton. The lower limb is attached to the vertebral column by the [pb_glossary id=\"2862\"]pelvic girdle[\/pb_glossary].<\/p>\r\n<p style=\"text-align: justify\">Because of our upright stance, different functional demands are placed upon the upper and lower limbs. Thus, the bones of the lower limbs are adapted for weight-bearing support and stability, as well as for body locomotion via walking or running. In contrast, our upper limbs are not required for these functions. Instead, our upper limbs are highly mobile and can be utilized for a wide variety of activities. The large range of upper limb movements, coupled with the ability to easily manipulate objects with our hands and opposable thumbs, has allowed humans to construct the modern world in which we live.<\/p>\r\n\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12B2a\"><\/a>The Pectoral Girdle<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The bones that attach each upper limb to the axial skeleton form the pectoral girdle (shoulder girdle). This consists of two bones, the scapula and clavicle (Figure 30).<\/p>\r\n<p style=\"text-align: justify\">The <strong>[pb_glossary id=\"2786\"]clavicle[\/pb_glossary]<\/strong> (collarbone) is an S-shaped bone located on the anterior side of the shoulder. It is attached on its [pb_glossary id=\"2362\"]medial[\/pb_glossary] end to the sternum of the thoracic cage, which is part of the axial skeleton. The lateral end of the clavicle articulates (joins) with the scapula just above the shoulder joint. You can easily palpate, or feel with your fingers, the entire length of your clavicle.<\/p>\r\n<p style=\"text-align: justify\">The <strong>[pb_glossary id=\"2755\"]scapula[\/pb_glossary]<\/strong> (shoulder blade) lies on the posterior aspect of the shoulder. It is supported by the clavicle, which also articulates with the [pb_glossary id=\"2746\"]humerus[\/pb_glossary] (upper arm bone) to form the shoulder joint. The scapula is a flat, triangular-shaped bone with a prominent ridge running across its [pb_glossary id=\"2358\"]posterior[\/pb_glossary] surface. This ridge extends out laterally, where it forms the bony tip of the shoulder and joins with the [pb_glossary id=\"2361\"]lateral[\/pb_glossary] end of the clavicle. By following along the clavicle, you can palpate out to the bony tip of the shoulder, and from there, you can move back across your posterior shoulder to follow the ridge of the scapula. Move your shoulder around and feel how the clavicle and scapula move together as a unit. Both of these bones serve as important attachment sites for muscles that aid with movements of the shoulder and arm. (Figures 30 &amp; 31)<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1028\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image32-4.png\" alt=\"image\" width=\"1028\" height=\"1047\" \/> <strong>Figure 29. Axial and Appendicular Skeletons.<\/strong> The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and thoracic cage. The appendicular skeleton consists of the pectoral and pelvic girdles, the limb bones, and the bones of the hands and feet.[\/caption]\r\n<p style=\"text-align: justify\">The right and left pectoral girdles are not joined to each other, allowing each to operate independently. In addition, the clavicle of each pectoral girdle is anchored to the axial skeleton by a single, highly mobile joint. This allows for the extensive mobility of the entire pectoral girdle, which in turn enhances movements of the shoulder and upper limb.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"760\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image33-4.png\" alt=\"image\" width=\"760\" height=\"1045\" \/> <strong>Figure 30. Pectoral Girdle.<\/strong> The pectoral girdle consists of the clavicle and the scapula, which serve to attach the upper limb to the sternum of the axial skeleton.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"971\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image34-4.png\" alt=\"image\" width=\"971\" height=\"640\" \/> <strong>Figure 31. Scapula.<\/strong> The isolated scapula is shown here from its anterior (deep) side and its posterior (superficial) side.[\/caption]\r\n<h5 style=\"text-align: justify\"><strong><a id=\"12B2b\"><\/a>Bones of the Upper Limb<\/strong><\/h5>\r\n<p style=\"text-align: justify\">The upper limb is divided into three regions. These consist of the <strong>arm<\/strong>, located between the shoulder and elbow joints; the <strong>forearm<\/strong>, which is between the elbow and wrist joints; and the <strong>hand<\/strong>, which is located distal to the wrist. There are 30 bones in each upper limb. The <strong>humerus<\/strong> is the single bone of the upper arm, and the <strong>[pb_glossary id=\"2745\"]ulna[\/pb_glossary]<\/strong> (medially) and the <strong>[pb_glossary id=\"2747\"]radius[\/pb_glossary]<\/strong> (laterally) are the paired bones of the forearm. The base of the hand contains eight bones, each called a <strong>[pb_glossary id=\"2752\"]carpal[\/pb_glossary] bone<\/strong>, and the palm of the hand is formed by five bones, each called a [pb_glossary id=\"2744\"]metacarpal[\/pb_glossary] bone. The fingers and thumb contain a total of 14 bones, each of which is a <strong>phalanx bone of the hand<\/strong>. (Figure 29)<\/p>\r\n<p style=\"text-align: justify\"><strong>Humerus:<\/strong> The humerus is the single bone of the upper arm region (Figure 32). At its proximal end is the head of the humerus. This is the large, round, smooth region that faces medially. The head articulates with the [pb_glossary id=\"2863\"]glenoid cavity[\/pb_glossary] of the scapula to form the [pb_glossary id=\"2864\"]glenohumeral[\/pb_glossary] (shoulder) joint. Distally, the humerus becomes flattened and has two articulation areas, which join the ulna and radius bones of the forearm to form the <strong>elbow joint<\/strong><\/p>\r\n<p style=\"text-align: justify\"><strong>Ulna:<\/strong> The ulna is the medial bone of the forearm. It runs parallel to the radius, which is the lateral bone of the forearm (Figure 33). The proximal end of the ulna articulates with the humerus as part of the elbow joint.<\/p>\r\n<p style=\"text-align: justify\"><strong>Radius:<\/strong> The radius runs parallel to the ulna, on the lateral (thumb) side of the forearm (Figure 33). The head of the radius is a disc-shaped structure that forms the [pb_glossary id=\"2373\"]proximal[\/pb_glossary] end. The distal end of the radius has a smooth surface for articulation with two carpal bones to form <strong>the [pb_glossary id=\"2865\"]radiocarpal joint[\/pb_glossary]<\/strong> or wrist joint (Figure 34 &amp; 35).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"673\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image35-5.png\" alt=\"image\" width=\"673\" height=\"847\" \/> <strong>Figure 32. Humerus and Elbow Joint.<\/strong> The humerus is the single bone of the upper arm region. It articulates with the radius and ulna bones of the forearm to form the elbow joint.[\/caption]\r\n\r\n<strong>Carpal Bones:<\/strong> The wrist and base of the hand are formed by a series of eight small carpal bones (Figure 34). The carpal bones are arranged in two rows, forming a proximal row of four carpal bones and a distal row of four carpal bones.\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"636\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image36-4.png\" alt=\"image\" width=\"636\" height=\"824\" \/> <strong>Figure 33. Ulna and Radius.<\/strong> The ulna is located on the medial side of the forearm, and the radius is on the lateral side. These bones are attached to each other by an interosseous membrane.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"976\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image37-4.png\" alt=\"image\" width=\"976\" height=\"783\" \/> <strong>Figure 34. Bones of the Wrist and Hand.<\/strong> The eight carpal bones form the base of the hand. These are arranged into proximal and distal rows of four bones each. The metacarpal bones form the palm of the hand. The thumb and fingers consist of the phalanx bones.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"968\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image38-5.png\" alt=\"image\" width=\"968\" height=\"585\" \/> <strong>Figure 35. Bones of the Hand.<\/strong> This radiograph shows the position of the bones within the hand. Note the carpal bones that form the base of the hand. (credit: modification of work by Trace Meek)[\/caption]\r\n<p style=\"text-align: justify\">The carpal bones form the base of the hand. This can be seen in the radiograph (X-ray image) of the hand that shows the relationships of the hand bones to the skin creases of the hand (Figure35).<\/p>\r\n<p style=\"text-align: justify\"><strong>Metacarpal Bones:<\/strong> The palm of the hand contains five elongated metacarpal bones. These bones lie between the carpal bones of the wrist and the bones of the fingers and thumb (Figure 34). The proximal end of each metacarpal bone articulates with one of the [pb_glossary id=\"2374\"]distal[\/pb_glossary] carpal bones. Each of these articulations is a carpometacarpal joint (Figure 35). The expanded distal end of each metacarpal bone articulates at the metacarpophalangeal joint with the proximal phalanx bone of the thumb or one of the fingers. The distal end also forms the knuckles of the hand, at the base of the fingers. The metacarpal bones are numbered 1\u20135, beginning at the thumb.<\/p>\r\n<p style=\"text-align: justify\"><strong>Phalanx Bones:<\/strong> The fingers and thumb contain 14 bones, each of which is called a [pb_glossary id=\"2750\"]phalanx[\/pb_glossary] bone (plural = phalanges), named after the ancient Greek phalanx (a rectangular block of soldiers). The thumb ([pb_glossary id=\"2405\"]pollex[\/pb_glossary]) is digit number 1 and has two phalanges, a proximal phalanx, and a distal phalanx bone (Figure 34). Digits 2 (index finger) through 5 (little finger) have three phalanges each, called the proximal, middle, and distal phalanx bones. An <strong>[pb_glossary id=\"2866\"]interphalangeal joint[\/pb_glossary]<\/strong> is one of the articulations between adjacent phalanges of the digits (Figure 35).<\/p>\r\n<p style=\"text-align: justify\"><strong>Part 3: The Pelvic Girdle and Pelvis<\/strong><\/p>\r\n<p style=\"text-align: justify\">The <strong>pelvic girdle<\/strong> (hip girdle) is formed by a single bone, the <strong>hip bone<\/strong> or <strong>coxal bone<\/strong> (coxal = \u201chip\u201d), which serves as the attachment point for each lower limb. Each hip bone, in turn, is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left hip bones also converge anteriorly to attach to each other. The bony <strong>pelvis<\/strong> is the entire structure formed by the two hip bones, the [pb_glossary id=\"2817\"]sacrum[\/pb_glossary], and the [pb_glossary id=\"2409\"]coccyx[\/pb_glossary] that is attached inferiorly to the sacrum (Figure 36).<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1151\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image39-4.png\" alt=\"image\" width=\"1151\" height=\"782\" \/> <strong>Figure 36. Pelvis.<\/strong> The pelvic girdle is formed by a single hip bone. The hip bone attaches the lower limb to the axial skeleton through its articulation with the sacrum. The right and left hip bones, plus the sacrum and the coccyx, together form the pelvis.[\/caption]\r\n<p style=\"text-align: justify\">Unlike the bones of the pectoral girdle, which are highly mobile to enhance the range of upper limb movements, the bones of the pelvis are strongly united to each other to form a largely immobile, weight-bearing structure. This is important for stability because it enables the weight of the body to be easily transferred laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb whenever the other limb is not bearing weight. Thus, the immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs.<\/p>\r\n<p style=\"text-align: justify\"><strong>Hip Bone:<\/strong> The hip bone, or coxal bone, forms the pelvic girdle portion of the pelvis. The paired hip bones are the large, curved bones that form the lateral and anterior aspects of the pelvis. Each adult hip bone is formed by three separate bones that fuse together during the late teenage years. These bony components are the [pb_glossary id=\"2867\"]ilium[\/pb_glossary], [pb_glossary id=\"2868\"]ischium[\/pb_glossary], and [pb_glossary id=\"2869\"]pubis[\/pb_glossary] (Figure 37). These names are retained and used to define the three regions of the adult hip bone.<\/p>\r\n<p style=\"text-align: justify\">The<strong> ilium<\/strong> is the fan-like, superior region that forms the largest part of the hip bone. It is firmly united to the sacrum at the largely immobile <strong>[pb_glossary id=\"2870\"]sacroiliac joint[\/pb_glossary]<\/strong> (Figure 36). The <strong>ischium<\/strong> forms the posteroinferior region of each hip bone. It supports the body when sitting. The <strong>pubis<\/strong> forms the anterior portion of the hip bone. The pubis curves medially, where it joins to the pubis of the opposite hip bone at a specialized joint called the <strong>[pb_glossary id=\"2871\"]pubic symphysis[\/pb_glossary]<\/strong>.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"973\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image40-4.png\" alt=\"image\" width=\"973\" height=\"698\" \/> <strong>Figure 37. The Hip Bone.<\/strong> The adult hip bone consists of three regions. The ilium forms the large, fan-shaped superior portion, the ischium forms the posteroinferior portion, and the pubis forms the anteromedial portion.[\/caption]\r\n<p style=\"text-align: justify\"><strong>Pelvis:<\/strong> The pelvis consists of four bones: the right and left hip bones, the sacrum, and the coccyx (Figure 36). The pelvis has several important functions. Its primary role is to support the weight of the upper body when sitting and to transfer this weight to the lower limbs when standing. It serves as an attachment point for trunk and lower limb muscles, and also protects the internal pelvic organs.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"953\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image41-4.png\" alt=\"image\" width=\"953\" height=\"447\" \/> <strong>Figure 38. Male and Female Pelves.<\/strong> The female pelvis is adapted for childbirth and is broader, with a larger subpubic angle, a rounder pelvic brim, and a wider and more shallow lesser pelvic cavity than the male pelvis.[\/caption]\r\n<p style=\"text-align: justify\"><strong>Comparison of the Female and Male Pelvis:<\/strong> The differences between the adult female and male pelvis relate to function and body size. In general, the bones of the male pelvis are thicker and heavier, adapted for support of the male\u2019s heavier physical build and stronger muscles; this average size difference is generally true of other bones of the skeleton as well. The pelvis does show more robust differences between males and females due to its functional relationship to bipedal movement (requiring a relatively narrow pelvis) and birth of infants with large brains (requiring a relatively broad pelvis). Because the female pelvis is adapted for childbirth, it is wider than the male pelvis, as evidenced by the distance between the anterior superior iliac spines (Figure 38). The [pb_glossary id=\"2872\"]ischial tuberosities[\/pb_glossary] of females are also farther apart, which increases the size of the pelvic outlet. Because of this increased pelvic width, the subpubic angle is larger in females (greater than 80 degrees) than it is in males (less than 70 degrees). The female sacrum is wider, shorter, and less curved, and the sacral promontory projects less into the pelvic cavity, thus giving the female pelvic inlet (pelvic brim) a more rounded or oval shape compared to males. The pelvic cavity of females is also wider and shallower than the narrower, deeper, and tapering lesser pelvis of males. The [pb_glossary id=\"2873\"]greater sciatic notch[\/pb_glossary] of the male hip bone is narrower and deeper than the broader notch of females. Because of the obvious differences between female and male hip bones, this is the one bone of the body that allows for the most accurate sex determination. Table 4 provides an overview of the general differences between the female and male pelvis.<\/p>\r\n\r\n<table style=\"border-collapse: collapse;width: 100%;height: 85px\" border=\"0\"><caption>Table 4: Overview of Differences Between Average Female and Male Pelves<\/caption>\r\n<tbody>\r\n<tr style=\"height: 14px\">\r\n<td style=\"width: 33.3333%;height: 14px\"><\/td>\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\"><strong>Female pelvis<\/strong><\/th>\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\"><strong>Male pelvis<\/strong><\/th>\r\n<\/tr>\r\n<tr style=\"height: 29px\">\r\n<th style=\"width: 33.3333%;height: 29px\" scope=\"row\"><strong>Pelvic weight<\/strong><\/th>\r\n<td style=\"width: 33.3333%;height: 29px\">Bones are lighter and thinner<\/td>\r\n<td style=\"width: 33.3333%;height: 29px\">Bones are thicker and heavier<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"row\"><strong>Pelvis inlet shape<\/strong><\/th>\r\n<td style=\"width: 33.3333%;height: 14px\">Round or oval<\/td>\r\n<td style=\"width: 33.3333%;height: 14px\">Heart-shaped<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"row\"><strong>Lesser pelvic cavity shape<\/strong><\/th>\r\n<td style=\"width: 33.3333%;height: 14px\">Shorter and wider<\/td>\r\n<td style=\"width: 33.3333%;height: 14px\">Longer and narrower<\/td>\r\n<\/tr>\r\n<tr style=\"height: 14px\">\r\n<th style=\"width: 33.3333%;height: 14px\" scope=\"row\"><strong>Subpubic angle<\/strong><\/th>\r\n<td style=\"width: 33.3333%;height: 14px\">Greater than 80 degrees<\/td>\r\n<td style=\"width: 33.3333%;height: 14px\">Less than 70 degrees<\/td>\r\n<\/tr>\r\n<tr>\r\n<th style=\"width: 33.3333%\" scope=\"row\"><strong>Pelvic outlet shape<\/strong><\/th>\r\n<td style=\"width: 33.3333%\">Rounded and larger<\/td>\r\n<td style=\"width: 33.3333%\">Smaller<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<p style=\"text-align: justify\"><strong>Part 4: Bones of the Lower Limb<\/strong><\/p>\r\n<p style=\"text-align: justify\">Like the upper limb, the lower limb is divided into three regions. The <strong>thigh<\/strong> is that portion of the lower limb located between the hip joint and knee joint. The <strong>leg<\/strong> is specifically the region between the knee joint and the ankle joint. Distal to the ankle is the <strong>foot<\/strong>. The lower limb contains 30 bones. These are the [pb_glossary id=\"2379\"]femur[\/pb_glossary], [pb_glossary id=\"2408\"]patella[\/pb_glossary], [pb_glossary id=\"2748\"]tibia[\/pb_glossary], [pb_glossary id=\"2749\"]fibula[\/pb_glossary], [pb_glossary id=\"2753\"]tarsal[\/pb_glossary] bones, [pb_glossary id=\"2743\"]metatarsal[\/pb_glossary] bones, and [pb_glossary id=\"2750\"]phalanges[\/pb_glossary] (Figure 29). The <strong>femur<\/strong> is the single bone of the thigh. The <strong>patella<\/strong> is the kneecap and articulates with the distal femur. The <strong>tibia<\/strong> is the larger, weight-bearing bone located on the medial side of the leg, and the <strong>fibula <\/strong>is the thin bone of the lateral leg. The bones of the foot are divided into three groups. The posterior portion of the foot is formed by a group of seven bones, each of which is known as a <strong>tarsal bone<\/strong>, whereas the mid-foot contains five elongated bones, each of which is a <strong>metatarsal bone<\/strong>. The toes contain 14 small bones, each of which is a <strong>phalanx bone of the foot<\/strong>.<\/p>\r\n<p style=\"text-align: justify\"><strong>Femur:<\/strong> The femur, or thigh bone, is the single bone of the thigh region (Figure 39). It is the longest and strongest bone of the body, and accounts for approximately one-quarter of a person\u2019s total height. The rounded, proximal end is the head of the femur, which articulates with the acetabulum of the hip bone to form the <strong>hip joint<\/strong>.<\/p>\r\n<p style=\"text-align: justify\"><strong>Patella:<\/strong> The [pb_glossary id=\"2408\"]patella[\/pb_glossary] (kneecap) is the largest [pb_glossary id=\"2874\"]sesamoid[\/pb_glossary] bone of the body (see Figure 39). A sesamoid bone is a bone that is incorporated into the tendon of a muscle where that tendon crosses a joint. The sesamoid bone articulates with the underlying bones to prevent damage to the muscle tendon due to rubbing against the bones during movements of the joint. The patella is found in the tendon of the [pb_glossary id=\"2875\"]quadriceps femoris[\/pb_glossary] muscle, the large muscle of the anterior thigh that passes across the anterior knee to attach to the tibia. The patella articulates with the patellar surface of the femur and thus prevents rubbing of the muscle tendon against the distal femur. The patella also lifts the tendon away from the knee joint, which increases the leverage power of the quadriceps femoris muscle as it acts across the knee. The patella does not articulate with the tibia.<\/p>\r\n<p style=\"text-align: justify\"><strong>Tibia:<\/strong> The [pb_glossary id=\"2748\"]tibia[\/pb_glossary] (shin bone) is the [pb_glossary id=\"2362\"]medial[\/pb_glossary] bone of the leg and is larger than the fibula, with which it is paired (Figure 40). The tibia is the main weight-bearing bone of the lower leg and the second longest bone of the body, after the [pb_glossary id=\"2379\"]femur[\/pb_glossary]. The medial side of the tibia is located immediately under the skin, allowing it to be easily palpated down the entire length of the medial leg.<\/p>\r\n<p style=\"text-align: justify\"><strong>Fibula:<\/strong> The fibula is the slender bone located on the lateral side of the leg (Figure 40). The fibula does not bear weight. It serves primarily for muscle attachments and thus is largely surrounded by muscles. Only the proximal and distal ends of the fibula can be palpated.<\/p>\r\n<p style=\"text-align: justify\"><strong>Tarsal Bones:<\/strong> The posterior half of the foot is formed by seven [pb_glossary id=\"2753\"]tarsal[\/pb_glossary] bones (Figure 43). The most superior tarsal bone, the<strong> [pb_glossary id=\"2876\"]talus[\/pb_glossary]<\/strong>, articulates with the tibia and fibula to form the <strong>ankle joint<\/strong>. Inferiorly, the talus articulates with the <strong>[pb_glossary id=\"2877\"]calcaneus[\/pb_glossary] <\/strong>(heel bone), the largest bone of the foot, which forms the heel. Body weight is transferred from the tibia to the talus to the calcaneus, which rests on the ground.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"669\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image43-4.png\" alt=\"image\" width=\"669\" height=\"1046\" \/> <strong>Figure 39. Femur and Patella.<\/strong> The femur is the single bone of the thigh region. It articulates superiorly with the hip bone at the hip joint, and inferiorly with the tibia at the knee joint. The patella only articulates with the distal end of the femur.[\/caption]\r\n<p style=\"text-align: justify\"><strong>Metatarsal Bones:<\/strong> The anterior half of the foot is formed by the five [pb_glossary id=\"2743\"]metatarsal[\/pb_glossary] bones, which are located between the tarsal bones of the posterior foot and the phalanges of the toes (Figure 41). These elongated bones are numbered 1\u20135, starting with the medial side of the foot.<\/p>\r\n<p style=\"text-align: justify\"><strong>Phalanx bones:<\/strong> The toes contain a total of 14 [pb_glossary id=\"2750\"]phalanx[\/pb_glossary] bones (phalanges), arranged in a similar manner as the phalanges of the fingers (Figure 41). The toes are numbered 1\u20135, starting with the big toe (<strong>[pb_glossary id=\"2404\"]hallux[\/pb_glossary]<\/strong>). The big toe has two phalanx bones, the proximal and distal phalanges. The remaining toes all have proximal, middle, and distal phalanges. A joint between adjacent phalanx bones is called an interphalangeal joint.<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"844\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image44-2.png\" alt=\"image\" width=\"844\" height=\"1044\" \/> <strong>Figure 40. Tibia and Fibula.<\/strong> The tibia is the larger, weight-bearing bone located on the medial side of the leg. The fibula is the slender bone of the lateral side of the leg and does not bear weight.[\/caption]\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"1118\"]<img src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image45-2.png\" alt=\"image\" width=\"1118\" height=\"814\" \/> <strong>Figure 41. Bones of the Foot.<\/strong> The bones of the foot are divided into three groups. The posterior foot is formed by the seven tarsal bones. The mid-foot has the five metatarsal bones. The toes contain the phalanges.[\/caption]\r\n\r\n<\/div>\r\n<div class=\"textbox textbox--exercises\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><a id=\"P\"><\/a>Practice Questions<\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\n<strong>A. Bone Tissue and the Skeletal System<\/strong>\r\n\r\n<strong>Part 1:<\/strong> The Functions of the Skeletal System\r\n\r\n[h5p id=\"10\"]\r\n\r\n<strong>Part 2: Bone Classification<\/strong>\r\n\r\n[h5p id=\"15\"]\r\n\r\n[h5p id=\"16\"]\r\n\r\n<strong>Part 3: Bone Structure<\/strong>\r\n\r\n[h5p id=\"11\"]\r\n\r\n[h5p id=\"12\"]\r\n\r\n[h5p id=\"13\"]\r\n\r\n[h5p id=\"14\"]\r\n\r\n[h5p id=\"17\"]\r\n\r\n[h5p id=\"21\"]\r\n\r\n[h5p id=\"22\"]\r\n\r\n<strong>Part 4: Bone Formation and Development<\/strong>\r\n\r\n[h5p id=\"18\"]\r\n\r\n[h5p id=\"19\"]\r\n\r\n[h5p id=\"40\"]\r\n\r\n[h5p id=\"23\"]\r\n\r\n[h5p id=\"25\"]\r\n\r\n[h5p id=\"39\"]\r\n\r\n[h5p id=\"26\"]\r\n\r\n[h5p id=\"28\"]\r\n\r\n[h5p id=\"30\"]\r\n\r\n<strong style=\"text-align: initial;font-size: 1em\">Part 5: Fractures<\/strong>\r\n\r\n[h5p id=\"31\"]\r\n\r\n[h5p id=\"32\"]\r\n\r\n<strong style=\"text-align: initial;font-size: 1em\">B. Skeletal Anatomy<\/strong>\r\n\r\n<strong style=\"text-align: initial;font-size: 1em\">Part 1: The <\/strong><strong style=\"text-align: initial;font-size: 1em\">Axial Skeleton<\/strong>\r\n\r\n[h5p id=\"33\"]\r\n\r\n[h5p id=\"34\"]\r\n\r\n[h5p id=\"35\"]\r\n\r\n[h5p id=\"37\"]\r\n\r\n[h5p id=\"36\"]\r\n\r\n[h5p id=\"41\"]\r\n\r\n<strong style=\"text-align: initial;font-size: 1em\">Part 2. The Appendicular Skeleton<\/strong>\r\n\r\n[h5p id=\"43\"]\r\n\r\n[h5p id=\"38\"]\r\n\r\n[h5p id=\"44\"]\r\n\r\n<\/div>\r\n<\/div>\r\n&nbsp;","rendered":"<div class=\"unit-12:-skeletal-system\">\n<div class=\"textbox shaded\">\n<p><strong>Unit outline<\/strong><\/p>\n<p><a href=\"#12A\"><strong>A. Bone Tissue and the Skeletal System<\/strong><\/a><\/p>\n<p><a href=\"#12A1\"><strong>Part 1:<\/strong> The Functions of the Skeletal System<\/a><\/p>\n<ul>\n<li><a href=\"#12A1a\">Support, movement, and protection<\/a><\/li>\n<li><a href=\"#12A1b\">Mineral storage, energy storage, and hematopoiesis<\/a><\/li>\n<\/ul>\n<p><a href=\"#12A2\"><strong>Part 2: <\/strong>Bone Classification<\/a><\/p>\n<p><a href=\"#12A3\"><strong>Part 3:<\/strong> Bone Structure<\/a><\/p>\n<ul>\n<li><a href=\"#12A3a\">Gross anatomy of bone<\/a><\/li>\n<li><a href=\"#12A3b\">Bone cells and tissues<\/a><\/li>\n<li><a href=\"#12A3c\">Compact and spongy bone<\/a><\/li>\n<li><a href=\"#12A3d\">Blood and nerve supply<\/a><\/li>\n<\/ul>\n<p><a href=\"#12A4\"><strong>Part 4: <\/strong>Bone Formation and Development<\/a><\/p>\n<ul>\n<li><a href=\"#12A4a\">Cartilage templates<\/a><\/li>\n<li><a href=\"#12A4b\">Intramembranous ossification<\/a><\/li>\n<li><a href=\"#12A4c\">Endochondral ossification<\/a><\/li>\n<li><a href=\"#12A4d\">How bones grow in length<\/a><\/li>\n<li><a href=\"#12A4e\">How bones grow in diameter<\/a><\/li>\n<li><a href=\"#12A4f\">Bone remodeling<\/a><\/li>\n<\/ul>\n<p><a href=\"#12A5\"><strong>Part 5:<\/strong> Fractures<\/a><\/p>\n<p>&nbsp;<\/p>\n<p><a href=\"#12B\"><strong>B. Skeletal Anatomy<\/strong><\/a><\/p>\n<p><a href=\"#12B1\"><strong style=\"text-align: initial;font-size: 1em\">Part 1: The<\/strong> <strong style=\"text-align: initial;font-size: 1em\">Axial Skeleton<\/strong><\/a><\/p>\n<ul>\n<li><a href=\"#12B1a\">The Skull<\/a><\/li>\n<li><a href=\"#12B1b\">The Vertebral Column<\/a><\/li>\n<li><a href=\"#12B1c\">The Thoracic Cage<\/a><\/li>\n<\/ul>\n<p><a href=\"#12B2\"><strong>Part 2. The Appendicular Skeleton<\/strong><\/a><\/p>\n<ul>\n<li><a href=\"#12B2a\">The Pectoral Girdle<\/a><\/li>\n<li><a href=\"#12B2b\">Bones of the Upper Limb<\/a><\/li>\n<li><a href=\"#12B2c\">The Pelvic Girdle and Pelvis<\/a><\/li>\n<li><a href=\"#12B2d\">Bones of the Lower Limb<\/a><\/li>\n<\/ul>\n<h2><a href=\"#P\">Practice Questions<\/a><\/h2>\n<\/div>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><strong>Learning Objectives<\/strong><\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p>At the end of this unit, you should be able to:<\/p>\n<p class=\"hanging-indent\"><strong>I.<\/strong> Describe the functions of the skeletal system and the five basic shapes of human bones.<\/p>\n<p class=\"hanging-indent\"><strong>II.<\/strong> Describe the structure and histology of the skeletal system.<\/p>\n<p class=\"hanging-indent\"><strong>III. <\/strong>Define and identify the following parts of a long bone: diaphysis, epiphysis, metaphysis, articular cartilage, periosteum, medullary cavity, and endosteum.<\/p>\n<p class=\"hanging-indent\"><strong>IV. <\/strong>Compare the composition and function of compact bone versus spongy bone.<\/p>\n<p class=\"hanging-indent\"><strong>V. <\/strong>Define ossification, compare intramembranous ossification with endochondral ossification, describe how a long bone grows in length and width, and specify how various factors might affect the rate of ossification and, by extension, the height of a mature individual.<\/p>\n<p class=\"hanging-indent\"><strong>VI. <\/strong>Specify the components of the axial and appendicular skeletons, describe the general function of each skeleton, and name and describe the principal components of the axial skeleton.<\/p>\n<p class=\"hanging-indent\"><strong>VII. <\/strong>Describe the structure and function of a typical vertebra and explain how these differ in the case of the atlas and axis.<\/p>\n<p class=\"hanging-indent\"><strong>VIII. <\/strong>Describe the components and functions of the pectoral girdle and the pelvic girdle.<\/p>\n<p class=\"hanging-indent\"><strong>IX.<\/strong> Specify all bones and structures in the human skeleton covered in this Unit.<\/p>\n<p class=\"hanging-indent\"><strong>X. <\/strong>Describe the differences between the pelvis of a human female and that of a human male.<\/p>\n<p class=\"hanging-indent\"><strong>XI. <\/strong>Describe the major differences between the skeleton of an infant and that of an adult.<\/p>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><strong>Learning Objectives and Guiding Questions<\/strong><\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p>At the end of this unit, you should be able to complete all the following tasks, including answering the guiding questions associated with each task.<\/p>\n<p class=\"hanging-indent\"><strong>I.<\/strong> Describe the functions of the skeletal system and the five basic shapes of human bones.<\/p>\n<ol>\n<li>Specify the ways that the skeletal system functions in the human body.<\/li>\n<li>The main common functions of all components of the human skeletal system are \u201cprotection\u201d and \u201csupport\u201d. Based on the material that follows in this Unit, select several examples of individual components (including both bone and cartilage examples) and describe how they serve each of these two functions.<\/li>\n<li>Name, describe, and provide one example of each of the five different shapes of human bones.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>II.<\/strong> Describe the structure and histology of the skeletal system.<\/p>\n<ol>\n<li class=\"no-indent\">Based on previously covered material and the information in this Unit, describe each of the different cell types found in cartilage and bone. For each cell type, identify:\n<ul>\n<li class=\"no-indent\">Where in the body, and from which type of cell, it arose.<\/li>\n<li class=\"no-indent\">Where it normally resides in the body, as specifically as possible.<\/li>\n<li class=\"no-indent\">What its main function is, and how (briefly) it serves that function.<\/li>\n<li class=\"no-indent\">What happens to the cell if the matrix that surrounds it calcifies.<\/li>\n<\/ul>\n<\/li>\n<li class=\"no-indent\">Based on previously covered material and the information in this Unit, compare and contrast the components of cartilage matrix and bone matrix, explaining the differences in the physical characteristics of cartilage and bone.<\/li>\n<li class=\"no-indent\">From what tissue type do bones and cartilage arise during early development? What other mature tissues arise from the same fetal tissue type?<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>III. <\/strong>Define and identify the following parts of a long bone: diaphysis, epiphysis, metaphysis, articular cartilage, periosteum, medullary cavity, and endosteum.<\/p>\n<ol>\n<li>Create a fully-labelled diagram of a typical long bone, showing the main external and internal features and identifying all the main tissue types found in a long bone.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>IV. <\/strong>Compare the composition and function of compact bone versus spongy bone.<\/p>\n<ol>\n<li class=\"hanging-indent\">Compare and contrast compact bone and spongy bone, in terms of the following characteristics:\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li class=\"hanging-indent\">The tissue type and cell type found in each type of bone.<\/li>\n<li class=\"hanging-indent\">The arrangement of tissue and\/or cells in each type of bone.<\/li>\n<li class=\"hanging-indent\">The location of each within a bone.<\/li>\n<li class=\"hanging-indent\">The function of each type of bone.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li class=\"hanging-indent\">Use annotated diagrams to compare and contrast the internal structure of an osteon with that of a trabecula.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>V. <\/strong>Define ossification, compare intramembranous ossification with endochondral ossification, describe how a long bone grows in length and width, and specify how various factors might affect the rate of ossification and, by extension, the height of a mature individual.<\/p>\n<ol>\n<li class=\"hanging-indent\">Explain in detail the processes of:\n<ul>\n<li class=\"hanging-indent\">Intramembranous ossification<\/li>\n<li class=\"hanging-indent\">Endochondral ossification<\/li>\n<li class=\"hanging-indent\">Growth in length of a long bone<\/li>\n<li class=\"hanging-indent\">Growth in width of a long bone<\/li>\n<\/ul>\n<\/li>\n<li class=\"hanging-indent\">Compare and contrast the processes of intramembranous ossification and endochondral ossification.<\/li>\n<li class=\"hanging-indent\">Compare and contrast the processes of endochondral ossification and lengthwise growth of a long bone.<\/li>\n<li class=\"hanging-indent\">Compare and contrast the processes of intramembranous ossification and widthwise growth of a long bone.<\/li>\n<li class=\"hanging-indent\">The height of an individual is largely determined by the rate of ossification prior to physical maturity. Briefly explain why this is so.<\/li>\n<li class=\"hanging-indent\">Based on information provided in this and other Units, briefly describe the effects you would expect to see, if any, on the height of an individual under the following conditions, and briefly explain your reasoning for each.\n<ul>\n<li class=\"hanging-indent\">Hypersecretion of growth hormone during development<\/li>\n<li class=\"hanging-indent\">Hyposecretion of growth hormone during development<\/li>\n<li class=\"hanging-indent\">Premature onset of puberty<\/li>\n<li class=\"hanging-indent\">Late onset of puberty<\/li>\n<li class=\"hanging-indent\">Shorter than average parents<\/li>\n<li class=\"hanging-indent\">Taller than average parents<\/li>\n<li class=\"hanging-indent\">Excessive caloric intake during development<\/li>\n<li class=\"hanging-indent\">Malnutrition during development<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<ol>\n<li class=\"hanging-indent\" style=\"list-style-type: none\"><\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>VI. <\/strong>Specify the components of the axial and appendicular skeletons, describe the general function of each skeleton, and name and describe the principal components of the axial skeleton.<\/p>\n<ol>\n<li class=\"hanging-indent\">List all the components of the axial skeleton.<\/li>\n<li class=\"hanging-indent\">List all the components of the appendicular skeleton.<\/li>\n<li class=\"hanging-indent\">Write one sentence that clearly describes and differentiates between the axial and appendicular skeletons.<\/li>\n<li class=\"hanging-indent\">Specify the main functions of the axial skeleton, and that of the appendicular skeleton. Explain how the overall shape of each skeleton is appropriate to its primary function.<\/li>\n<li>Describe the location of the following:\n<ul>\n<li>Xiphoid process of the sternum<\/li>\n<li>Mastoid process of the temporal bone<\/li>\n<\/ul>\n<\/li>\n<li>Describe in general terms the location and function of the following:\n<ul>\n<li class=\"hanging-indent\">Hyoid bone<\/li>\n<li class=\"hanging-indent\">Incus, malleus, and stapes<\/li>\n<li class=\"hanging-indent\">Atlas<\/li>\n<li class=\"hanging-indent\">Axis<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>VII. <\/strong>Describe the structure and function of a typical vertebra and explain how these differ in the case of the atlas and axis.<\/p>\n<ol>\n<li class=\"hanging-indent\">Sketch a diagram of a typical vertebra, clearly showing and labelling all the following components:\n<ul>\n<li class=\"hanging-indent\">Body<\/li>\n<li class=\"hanging-indent\">Vertebral foramen<\/li>\n<li class=\"hanging-indent\">Transverse processes<\/li>\n<li class=\"hanging-indent\">Spinous process<\/li>\n<\/ul>\n<\/li>\n<li class=\"hanging-indent\">Sketch a diagram of the atlas and of the axis, clearly showing and labelling the following components, where applicable:\n<ul>\n<li class=\"hanging-indent\">Body<\/li>\n<li class=\"hanging-indent\">Vertebral foramen<\/li>\n<li class=\"hanging-indent\">Transverse processes<\/li>\n<li class=\"hanging-indent\">Spinous process<\/li>\n<li class=\"hanging-indent\">Dens<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>VIII. <\/strong>Describe the components and functions of the pectoral girdle and the pelvic girdle.<\/p>\n<ol>\n<li class=\"hanging-indent\">List the bones that make up in the pectoral girdle. Identify each as being part of the appendicular or axial skeleton.<\/li>\n<li class=\"hanging-indent\">List the bones and cartilage that make up the pelvic girdle. Identify each as being part of the appendicular or axial skeleton.<\/li>\n<li class=\"hanging-indent\">Compare and contrast the location, structure, and function of the pectoral girdle and the pelvic girdle. What about them is similar? What differs?<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>IX.<\/strong> Specify all bones and structures in the human skeleton covered in this Unit.<\/p>\n<ol>\n<li>Locate and identify the following bones in a diagram of a human skeleton:\n<ul>\n<li>Frontal bone<\/li>\n<li>Parietal bone<\/li>\n<li>Temporal bone<\/li>\n<li>Occipital bone<\/li>\n<li>Mandible<\/li>\n<li>Maxilla<\/li>\n<li>Cervical vertebrae<\/li>\n<li>Thoracic vertebrae<\/li>\n<li>Lumbar vertebrae<\/li>\n<li>Sacrum<\/li>\n<li>Coccyx<\/li>\n<li>True ribs<\/li>\n<li>False ribs<\/li>\n<li>Floating ribs<\/li>\n<li>Sternum<\/li>\n<li>Clavicle<\/li>\n<li>Scapula<\/li>\n<li>Humerus<\/li>\n<li>Radius<\/li>\n<li>Ulna<\/li>\n<li>Carpals<\/li>\n<li>Metacarpals<\/li>\n<li>Phalanges<\/li>\n<li>Hip bone<\/li>\n<li>Femur<\/li>\n<li>Patella<\/li>\n<li>Tibia<\/li>\n<li>Fibula<\/li>\n<li>Tarsals<\/li>\n<li>Metatarsals<\/li>\n<\/ul>\n<\/li>\n<li>Sketch a human skeleton from memory. Label all the large long bones, and all the visible cartilages. Check your sketch against your textbook and worksheet to see if you\u2019ve missed anything.<\/li>\n<li>By external examination (look and feel), determine the location of your own:\n<ul>\n<li class=\"hanging-indent\">Phalanges<\/li>\n<li class=\"hanging-indent\">Metacarpals and metatarsals<\/li>\n<li class=\"hanging-indent\">Carpals and tarsals<\/li>\n<li class=\"hanging-indent\">Humerus and femur<\/li>\n<li class=\"hanging-indent\">Patella<\/li>\n<li class=\"hanging-indent\">Ulna, radius, tibia, and fibula<\/li>\n<li class=\"hanging-indent\">True ribs, false ribs, and floating ribs<\/li>\n<li class=\"hanging-indent\">Sternum<\/li>\n<li class=\"hanging-indent\">Clavicle and scapula<\/li>\n<li class=\"hanging-indent\">Iliac crest of the hip bone<\/li>\n<li class=\"hanging-indent\">Maxilla and mandible<\/li>\n<li class=\"hanging-indent\">Frontal bone and occipital bone<\/li>\n<li class=\"hanging-indent\">Sacrum<\/li>\n<li class=\"hanging-indent\">Spinous process of a vertebra<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>X. <\/strong>Describe the differences between the pelvis of a human female and that of a human male.<\/p>\n<ol>\n<li>Describe the differences between an average male pelvis and an average female pelvis.<\/li>\n<li>Why are male and female pelves generally shaped differently? For each sex difference noted in the question above, briefly explain the functional relevance of that sex difference specifically.<\/li>\n<\/ol>\n<p class=\"hanging-indent\"><strong>XI. <\/strong>Describe the major differences between the skeleton of an infant and that of an adult.<\/p>\n<ol>\n<li>Describe the difference in tissue composition (relative amounts of different tissue types) of the skeleton of a child and that of an adult.<\/li>\n<li>Explain why the skeleton of a newborn contains more bones than that of an adult, by naming two examples of bones that are formed by fully fusing two or more pieces of bone tissue.<\/li>\n<li>Describe the difference in relative body proportions between the skeleton of an infant and that of an adult.<\/li>\n<li>Describe the differences between the skull of a newborn and that of an adult.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<h1 style=\"text-align: justify\"><strong><a id=\"12A\"><\/a>A. Bone Tissue and the Skeletal System<\/strong><\/h1>\n<p style=\"text-align: justify\">Your skeleton is a structure of living tissue that grows, repairs, and renews itself. The bones within it are dynamic and complex organs that serve a number of important functions, including some necessary to maintain homeostasis.<\/p>\n<p style=\"text-align: justify\">The skeletal system forms the rigid internal framework of the body. It consists of the bones, cartilages, and ligaments. Bones support the weight of the body, allow for body movements, and protect internal organs. Cartilage provides flexible strength and support for body structures such as the thoracic cage, the external ear, and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2737\">trachea<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2738\">larynx<\/a>. At joints of the body, cartilage can also unite adjacent bones or provide cushioning between them. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2735\">Ligaments<\/a> are the strong connective tissue bands that hold the bones at a moveable joint together and serve to prevent excessive movements of the joint that would result in injury. Providing movement of the skeleton are the muscles of the body, which are firmly attached to the skeleton via connective tissue structures called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2736\">tendons<\/a>. As muscles contract, they pull on the bones to produce movements of the body. Thus, without a skeleton, you would not be able to stand, run, or even feed yourself!<\/p>\n<p style=\"text-align: justify\">Each bone of the body serves a particular function, and therefore bones vary in size, shape, and strength based on these functions. For example, the bones of the lower back and lower limb are thick and strong to support your body weight. Similarly, the size of a bony landmark that serves as a muscle attachment site on an individual bone is related to the strength of this muscle. Muscles can apply very strong pulling forces to the bones of the skeleton. To resist these forces, bones have enlarged bony landmarks at sites where powerful muscles attach. This means that not only the size of a bone, but also its shape, is related to its function. Bones are also dynamic organs that can modify their strength and thickness in response to changes in muscle strength or body weight. Thus, muscle attachment sites on bones will thicken if you begin a workout program that increases muscle strength. Similarly, the walls of weight-bearing bones will thicken if you gain body weight or begin pounding the pavement as part of a new running regimen. In contrast, a reduction in muscle strength or body weight will cause bones to become thinner. This may happen during a prolonged hospital stay, following limb immobilization in a cast, or going into the weightlessness of outer space. Even a change in diet, such as eating only soft food due to the loss of teeth, will result in a noticeable decrease in the size and thickness of the jaw bones.<\/p>\n<h2 style=\"text-align: justify\"><strong><a id=\"12A1\"><\/a>Part 1: The Functions of the Skeletal System<\/strong><\/h2>\n<p style=\"text-align: justify\">Bone, or osseous tissue, is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body. In the areas of the skeleton where bones move (for example, the ribcage and joints), cartilage, a semi-rigid form of connective tissue, provides flexibility and smooth surfaces for movement. The skeletal system is the body system composed of bones and cartilage and performs the following critical functions for the human body:<\/p>\n<ul>\n<li>supports the body<\/li>\n<li>facilitates movement<\/li>\n<li>protects internal organs<\/li>\n<li>produces blood cells<\/li>\n<li>stores and releases minerals and fat<\/li>\n<\/ul>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A1a\"><\/a>Support, Movement and Protection<\/strong><\/h5>\n<p style=\"text-align: justify\">The most apparent functions of the skeletal system are the gross functions\u2014those visible by observation. Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body.<\/p>\n<p style=\"text-align: justify\">Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin.<\/p>\n<p style=\"text-align: justify\">Bones also facilitate movement by serving as points of attachment for your muscles. While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract. From a mechanical point of view, bones act as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2739\">levers<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2740\">joints<\/a> serve as fulcrums (Figure 1). Unless a muscle spans a joint and contracts, a bone is not going to move.<\/p>\n<figure style=\"width: 537px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image1-6.png\" alt=\"image\" width=\"537\" height=\"761\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 1. Bones Support Movement.<\/strong> Bones act as levers when muscles span a joint and contract. (credit: Benjamin J. DeLong)<\/figcaption><\/figure>\n<figure style=\"width: 621px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image2-6.png\" alt=\"image\" width=\"621\" height=\"804\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 2. Bones Protect the Brain.<\/strong> The cranium completely surrounds and protects the brain from non-traumatic injury.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">Bones also protect internal organs from injury by covering or surrounding them. For example, your ribs protect your lungs and heart, the bones of your vertebral column (spine) protect your spinal cord, and the bones of your cranium (skull) protect your brain (Figure 2).<\/p>\n<p style=\"text-align: justify\"><strong>Mineral Storage, Energy Storage, and Hematopoiesis:<\/strong> On a metabolic level, bone tissue performs several critical functions. For one, the bone matrix (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2298\">ground substance<\/a>) acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and phosphorus. These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes. Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses.<\/p>\n<p style=\"text-align: justify\">Bone also serves as a site for fat storage and blood cell production. The softer connective tissue that fills the interior of most bone is referred to as bone marrow (Figure 3). There are two types of bone marrow: yellow marrow and red marrow. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2742\">Yellow marrow<\/a> contains <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2300\">adipose<\/a> tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of energy. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2741\">Red marrow<\/a> is where <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2329\">hematopoiesis<\/a>\u2014the production of blood cells\u2014takes place. Red blood cells, white blood cells, and cell fragments called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2328\">platelets<\/a> are all produced in the red marrow.<\/p>\n<figure style=\"width: 660px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image3-7.png\" alt=\"image\" width=\"660\" height=\"394\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 3. Head of the Femur Showing Red and Yellow Marrow.<\/strong> The head of the femur contains both yellow and red marrow. Yellow marrow stores fat. Red marrow is responsible for hematopoiesis. (credit: modification of work by \u201cstevenfruitsmaak\u201d\/Wikimedia Commons)<\/figcaption><\/figure>\n<h2 style=\"text-align: justify\"><strong><a id=\"12A2\"><\/a>Part 2: Bone Classification<\/strong><\/h2>\n<p style=\"text-align: justify\">The 206 bones that compose the adult skeleton can be divided into five categories based on their shapes (Figure 4). Their shapes and their functions are related such that each categorical shape of bone has a distinct function.<\/p>\n<p style=\"text-align: justify\"><strong>Long Bones:<\/strong> A long bone is one that is cylindrical in shape, with a diameter smaller than its height. Keep in mind, however, that the term describes the shape of a bone, not its size. Long bones are found in the arms (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2746\">humerus<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2745\">ulna<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2747\">radius<\/a>) and legs (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2379\">femur<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2748\">tibia<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2749\">fibula<\/a>), as well as in the fingers (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2744\">metacarpals<\/a> and phalanges) and toes (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2743\">metatarsals<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2750\">phalanges<\/a>). Long bones function as levers; they move when muscles contract.<\/p>\n<p style=\"text-align: justify\"><strong>Short Bones:<\/strong> A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness. The only short bones in the human skeleton are in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2752\">carpals<\/a> of the wrists and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2753\">tarsals<\/a> of the ankles. Short bones provide stability and support as well as some limited motion.<\/p>\n<p style=\"text-align: justify\"><strong>Flat Bones:<\/strong> The term \u201cflat bone\u201d is somewhat of a misnomer because, although a flat bone is typically thin, it is also often curved. Examples include the cranial bones of the skull, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2755\">scapulae<\/a> (shoulder blades), the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2754\">sternum<\/a> (breastbone), and the ribs. Flat bones serve as points of attachment for muscles and often protect internal organs.<\/p>\n<p style=\"text-align: justify\"><strong>Irregular Bones:<\/strong> An irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification. These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Many facial bones, particularly the ones containing sinuses, are classified as irregular bones.<\/p>\n<p style=\"text-align: justify\"><strong>Sesamoid Bones:<\/strong> A sesamoid bone is a small, round bone that, as the name suggests, is shaped like a sesame seed. These bones form in tendons (the sheaths of tissue that connect bones to muscles) where a great deal of pressure is generated in a joint. The sesamoid bones protect <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2736\">tendons<\/a> by helping them overcome compressive forces. Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and knees. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2408\">patellae<\/a> (singular = patella) are the only sesamoid bones found in common with every person. Table 1 reviews bone classifications with their associated features, functions, and examples.<\/p>\n<table style=\"border-collapse: collapse;width: 100%\">\n<caption>Table 1: Bone Classification by Shape<\/caption>\n<tbody>\n<tr>\n<th style=\"width: 25%\" scope=\"col\"><strong>Bone classification<\/strong><\/th>\n<th style=\"width: 25%\" scope=\"col\"><strong>Features<\/strong><\/th>\n<th style=\"width: 25%\" scope=\"col\"><strong>Function(s)<\/strong><\/th>\n<th style=\"width: 25%\" scope=\"col\"><strong>Examples<\/strong><\/th>\n<\/tr>\n<tr>\n<td style=\"width: 25%\">Long<\/td>\n<td style=\"width: 25%\">Cylinder-like shape, longer than it is wide<\/td>\n<td style=\"width: 25%\">Leverage<\/td>\n<td style=\"width: 25%\">Femur, tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges<\/td>\n<\/tr>\n<tr>\n<td style=\"width: 25%\">Short<\/td>\n<td style=\"width: 25%\">Cube-like shape, approximately equal in length, width, and thickness<\/td>\n<td style=\"width: 25%\">Provide stability &amp; support while allowing for some motion<\/td>\n<td style=\"width: 25%\">Carpals, tarsals<\/td>\n<\/tr>\n<tr>\n<td style=\"width: 25%\">Flat<\/td>\n<td style=\"width: 25%\">Thin and curved<\/td>\n<td style=\"width: 25%\">Points of attachment for muscles; protectors of internal organs<\/td>\n<td style=\"width: 25%\">Sternum, ribs, scapulae, cranial bones<\/td>\n<\/tr>\n<tr>\n<td style=\"width: 25%\">Irregular<\/td>\n<td style=\"width: 25%\">Complex shape<\/td>\n<td style=\"width: 25%\">Protect internal organs<\/td>\n<td style=\"width: 25%\">Vertebrae, facial bones<\/td>\n<\/tr>\n<tr>\n<td style=\"width: 25%\">Sesamoid<\/td>\n<td style=\"width: 25%\">Small and round; embedded in tendons<\/td>\n<td style=\"width: 25%\">Protect tendons from compressive forces<\/td>\n<td style=\"width: 25%\">Patellae<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2 style=\"text-align: justify\"><strong><a id=\"12A3\"><\/a>Part 3: Bone Structure<\/strong><\/h2>\n<p style=\"text-align: justify\">Bone tissue (osseous tissue) differs greatly from other tissues in the body. Bone is hard and many of its functions depend on that characteristic hardness. Later discussions in this chapter will show that bone is also dynamic in that its shape adjusts to accommodate stresses. This section will examine the gross anatomy of bone first and then move on to its histology.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A3a\"><\/a>Gross Anatomy of Bone<\/strong><\/h5>\n<p style=\"text-align: justify\">The structure of a long bone allows for the best visualization of all of the parts of a bone (Figure 5). A long bone has two parts: the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2756\">diaphysis<\/a><\/strong> and the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2757\">epiphysis<\/a><\/strong>. The diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone. The hollow region in the diaphysis is called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2758\">medullary cavity<\/a><\/strong>, which is filled with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2742\">yellow marrow<\/a>. The walls of the diaphysis are composed of dense and hard <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2759\">compact bone<\/a><\/strong>. The wider section at each end of the bone is called the <strong>epiphysis<\/strong> (plural = epiphyses), which is filled with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2327\">spongy bone<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2741\">Red marrow<\/a> fills the spaces in the spongy bone.<\/p>\n<figure style=\"width: 903px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image5-6.png\" alt=\"image\" width=\"903\" height=\"1045\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 4. Classifications of Bones.<\/strong> Bones can be classified according to their shape.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">Each epiphysis meets the diaphysis at the metaphysis, the narrow area that contains the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2760\">epiphyseal plate<\/a><\/strong> (growth plate), a layer of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2321\">hyaline<\/a> (transparent) cartilage in a growing bone. When the bone stops growing in early adulthood (approximately 18\u201321 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2761\">epiphyseal line<\/a>.<\/p>\n<p style=\"text-align: justify\">The medullary cavity has a delicate membranous lining called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2762\">endosteum<\/a> <\/strong>(end- = \u201cinside\u201d; oste- = \u201cbone\u201d), where bone growth, repair, and remodeling occur. The outer surface of the bone is covered with a fibrous membrane called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2764\">periosteum<\/a> <\/strong>(peri\u2013 = \u201caround\u201d or \u201csurrounding\u201d). The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Tendons and ligaments also attach to bones at the periosteum. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints (Figure 6). In this region, the epiphyses are covered with <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2763\">articular cartilage<\/a><\/strong>, a thin layer of cartilage that reduces friction and acts as a shock absorber.<\/p>\n<figure style=\"width: 619px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image6-6.png\" alt=\"image\" width=\"619\" height=\"1048\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 5. Anatomy of a Long Bone.<\/strong> A typical long bone shows the gross anatomical characteristics of bone.<\/figcaption><\/figure>\n<figure style=\"width: 1069px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image7-6.png\" alt=\"image\" width=\"1069\" height=\"535\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 6. Periosteum and Endosteum.<\/strong> The periosteum forms the outer surface of bone, and the endosteum lines the internal surfaces of bone, like the medullary cavity.<\/figcaption><\/figure>\n<figure style=\"width: 811px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image8-7.png\" alt=\"image\" width=\"811\" height=\"409\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 7. Anatomy of a Flat Bone.<\/strong> This cross-section of a flat bone shows the spongy bone (diplo\u00eb) lined on either side by a layer of compact bone.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">Flat bones, like those of the cranium, consist of a layer of <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2765\">diplo\u00eb<\/a><\/strong> (spongy bone), lined on either side by a layer of compact bone (Figure 7). The two layers of compact bone and the interior spongy bone work together to protect the internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A3b\"><\/a>Bone Cells and Tissue<\/strong><\/h5>\n<p style=\"text-align: justify\">Bone contains a relatively small number of cells entrenched in a matrix of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2174\">collagen<\/a> fibres that provide a surface for inorganic salt crystals to adhere. These salt crystals, made of a substance called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2324\">hydroxyapatite<\/a>, form when calcium phosphate and calcium carbonate combine with other inorganic salts and solidify, (i.e. calcify) on the collagen fibres. The crystals give bones their hardness and strength, while the collagen fibres give them flexibility so that they are not brittle.<\/p>\n<p style=\"text-align: justify\">Although bone cells compose a small amount of the bone volume, they are crucial to the function of bones. Four types of cells are found within bone tissue: osteoblasts, osteocytes, osteogenic cells, and osteoclasts (Figure 8).<\/p>\n<p style=\"text-align: justify\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2766\">osteoblast<\/a><\/strong> is the bone cell responsible for forming new bone and is found in the growing portions of bone, including the periosteum and endosteum. Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and calcium salts. As the secreted matrix surrounding the osteoblast calcifies, the osteoblast become trapped within it; as a result, it changes in structure and becomes an <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2325\">osteocyte<\/a><\/strong>, the primary cell of mature bone and the most common type of bone cell. Each osteocyte is located in a space called a<strong> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2318\">lacuna<\/a><\/strong> and is surrounded by bone matrix. Osteocytes maintain the mineral concentration of the matrix. Like osteoblasts, osteocytes lack mitotic activity. They can communicate with each other and receive nutrients via long cytoplasmic processes that extend through <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2767\">canaliculi<\/a><\/strong> (singular = canaliculus), channels within the bone matrix.<\/p>\n<figure style=\"width: 807px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image9-6.png\" alt=\"image\" width=\"807\" height=\"564\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 8. Bone Cells.<\/strong> Four types of cells are found within bone tissue. Osteogenic cells are undifferentiated and develop into osteoblasts. When osteoblasts get trapped within the calcified matrix, their structure and function changes, and they become osteocytes. Osteoclasts develop from monocytes and macrophages and differ in appearance from other bone cells.<\/figcaption><\/figure>\n<p>If osteoblasts and osteocytes are incapable of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2709\">mitosis<\/a>, then how are they replenished when old ones die? The answer lies in the properties of a third category of bone cells\u2014the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2770\">osteogenic cell<\/a><\/strong>. These osteogenic cells are undifferentiated with high mitotic activity and they are the only bone cells that divide. Immature osteogenic cells are found in the deep layers of the periosteum and the marrow. They differentiate and develop into osteoblasts.<\/p>\n<p style=\"text-align: justify\">The dynamic nature of bone means that new tissue is constantly formed, and old, injured, or unnecessary bone is dissolved for repair or for calcium release. The cell responsible for bone resorption, or breakdown, is the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2768\">osteoclast<\/a><\/strong>. They are found on bone surfaces, are multinucleated, and originate from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2769\">monocytes<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2307\">macrophages<\/a>, two types of white blood cells, not from osteogenic cells. Osteoclasts are continually breaking down old bone while osteoblasts are continually forming new bone. The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone. Table 2 reviews the bone cells, their functions, and locations.<\/p>\n<table style=\"border-collapse: collapse;width: 100%;height: 70px\">\n<caption>Table 2: Bone Cells<\/caption>\n<tbody>\n<tr style=\"height: 14px\">\n<th style=\"width: 18.9265%;height: 14px\" scope=\"col\"><strong>Cell type<\/strong><\/th>\n<th style=\"width: 33.1921%;height: 14px\" scope=\"col\"><strong>Function<\/strong><\/th>\n<th style=\"width: 47.8813%;height: 14px\" scope=\"col\"><strong>Location<\/strong><\/th>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 18.9265%;height: 14px\">Osteogenic cells<\/td>\n<td style=\"width: 33.1921%;height: 14px\">Develop into osteoblasts<\/td>\n<td style=\"width: 47.8813%;height: 14px\">Deep layers of the periosteum and the marrow<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 18.9265%;height: 14px\">Osteoblasts<\/td>\n<td style=\"width: 33.1921%;height: 14px\">Bone formation<\/td>\n<td style=\"width: 47.8813%;height: 14px\">Growing portions of bone, including periosteum and endosteum<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 18.9265%;height: 14px\">Osteocytes<\/td>\n<td style=\"width: 33.1921%;height: 14px\">Maintain mineral concentration of matrix<\/td>\n<td style=\"width: 47.8813%;height: 14px\">Entrapped in matrix (in lacunae)<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 18.9265%;height: 14px\">Osteoclasts<\/td>\n<td style=\"width: 33.1921%;height: 14px\">Bone resorption<\/td>\n<td style=\"width: 47.8813%;height: 14px\">Bone surfaces and at sites of old, injured, or unneeded bone<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h5><strong><a id=\"12A3c\"><\/a>Compact and Spongy Bone<\/strong><\/h5>\n<p>The differences between compact and spongy bone are best explored via their histology. Most bones contain compact and spongy osseous tissue, but their distribution and concentration vary based on the bone\u2019s overall function. Compact bone is dense so that it can withstand compressive forces, while spongy (cancellous) bone has open spaces and supports shifts in weight distribution.<\/p>\n<p style=\"text-align: justify\"><strong>1. Compact Bone:<\/strong> Compact bone is the denser, stronger of the two types of bone tissue (Figure 9). It can be found deep to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2764\">periosteum<\/a> and in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2756\">diaphyses<\/a> of long bones, where it provides support and protection.<\/p>\n<p style=\"text-align: justify\">The microscopic structural unit of compact bone is called an<strong> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2771\">osteon<\/a><\/strong>, or Haversian system. Each osteon is composed of concentric rings of calcified matrix called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2774\">lamellae<\/a> (singular = lamella). Running down the center of each osteon is the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2772\">central canal<\/a><\/strong>, or Haversian canal, which contains blood vessels, nerves, and lymphatic vessels. These vessels and nerves branch off at right angles through a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2773\">perforating canal<\/a><\/strong>, also known as Volkmann\u2019s canals, to extend to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2764\">periosteum<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2762\">endosteum<\/a>.<\/p>\n<p style=\"text-align: justify\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2325\">osteocytes<\/a> are located inside spaces called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2318\">lacunae<\/a> (singular = lacuna), found at the borders of adjacent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2774\">lamellae<\/a>. As described earlier, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2767\">canaliculi<\/a> connect with the canaliculi of other lacunae and eventually with the central canal. This system allows nutrients to be transported to the osteocytes and wastes to be removed from them.<\/p>\n<p style=\"text-align: justify\"><strong>2. Spongy (Cancellous) Bone:<\/strong> Like compact bone, <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2327\">spongy bone<\/a>,<\/strong> also known as cancellous bone, contains osteocytes housed in lacunae, but they are not arranged in concentric circles. Instead, the lacunae and osteocytes are found in a lattice-like network of matrix spikes called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2775\">trabeculae<\/a><\/strong> (singular = trabecula) (Figure 10). The trabeculae may appear to be a random network, but each trabecula forms along lines of stress to provide strength to the bone. The spaces of the trabeculated network provide balance to the dense and heavy compact bone by making bones lighter so that muscles can move them more easily. In addition, the spaces in some spongy bones contain red marrow, protected by the trabeculae, where <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2329\">hematopoiesis<\/a> occurs.<\/p>\n<figure style=\"width: 889px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image11-6.png\" alt=\"image\" width=\"889\" height=\"1044\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 9. Compact Bone.<\/strong> (a) This cross-sectional view of compact bone shows the basic structural unit, the osteon. (b) In this micrograph of the osteon, you can clearly see the concentric lamellae and central canals. LM \u00d7 40. (Micrograph provided by the Regents of University of Michigan Medical School \u00a9 2012)<\/figcaption><\/figure>\n<figure style=\"width: 1117px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image12-6.png\" alt=\"image\" width=\"1117\" height=\"739\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 10. Spongy Bone.<\/strong> Spongy bone is composed of trabeculae that contain the osteocytes. Red marrow fills the spaces in some bones.<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A3d\"><\/a>Blood and Nerve Supply<\/strong><\/h5>\n<p style=\"text-align: justify\">The spongy bone and medullary cavity receive nourishment from arteries that pass through the compact bone. The arteries enter through the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2783\">nutrient foramen<\/a><\/strong> (plural = foramina), a small opening in the diaphysis (Figure 11). The osteocytes in spongy bone are nourished by blood vessels of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2764\">periosteum<\/a> that penetrate spongy bone and blood that circulates in the marrow cavities. As the blood passes through the marrow cavities, it is collected by veins, which then pass out of the bone through the foramen.<\/p>\n<p style=\"text-align: justify\">In addition to the blood vessels, nerves follow the same paths into the bone where they tend to concentrate in the more metabolically active regions of the bone. The nerves sense pain, and it appears the nerves also play roles in regulating blood supplies and in bone growth, hence their concentrations in metabolically active sites of the bone.<\/p>\n<figure style=\"width: 579px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image13-6.png\" alt=\"image\" width=\"579\" height=\"807\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 11. Blood and Nerve Supply to Bone.<\/strong> Blood vessels and nerves enter the bone through the nutrient foramen.<\/figcaption><\/figure>\n<h2 style=\"text-align: justify\"><strong><a id=\"12A4\"><\/a>Part 4: Bone Formation and Development<\/strong><\/h2>\n<p style=\"text-align: justify\">In the early stages of embryonic development, the embryo\u2019s skeleton consists of fibrous membranes and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2321\">hyaline cartilage<\/a>. By the sixth or seventh week of embryonic life, the actual process of bone development, <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2784\">ossification<\/a><\/strong> (osteogenesis), begins. There are two osteogenic pathways\u2014<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2785\">intramembranous ossification<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2792\">endochondral ossification<\/a>\u2014but bone is the same regardless of the pathway that produces it.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4a\"><\/a>Cartilage Templates<\/strong><\/h5>\n<p style=\"text-align: justify\">Bone is a replacement tissue; that is, it uses a model tissue on which to lay down its mineral matrix. For skeletal development, the most common template is cartilage. During fetal development, a framework is laid down that determines where bones will form. This framework is a flexible, semi-solid cartilage matrix produced by chondroblasts. As the matrix surrounds and isolates <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2788\">chondroblasts<\/a>, they mature into cells called chondrocytes. Unlike most connective tissues, cartilage is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2286\">avascular<\/a>, meaning that it has no blood vessels supplying nutrients and removing metabolic wastes. All of these functions are carried on by diffusion through the matrix. This is why damaged cartilage does not repair itself as readily as most tissues do.<\/p>\n<p style=\"text-align: justify\">Throughout fetal development and into childhood growth and development, bone forms on the cartilaginous matrix. By the time a fetus is born, most of the cartilage has been replaced with bone. Some additional cartilage will be replaced throughout childhood, and some cartilage remains in the adult skeleton.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4b\"><\/a>Intramembranous Ossification<\/strong><\/h5>\n<p style=\"text-align: justify\">During <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2785\">intramembranous ossification<\/a><\/strong>, compact and spongy bone develops directly from sheets of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2306\">mesenchymal<\/a> (undifferentiated) connective tissue. The flat bones of the face, most of the cranial bones, and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2786\">clavicles<\/a> (collarbones) are initially formed via intramembranous ossification.<\/p>\n<p style=\"text-align: justify\">The process begins when mesenchymal cells in the embryonic skeleton gather together and begin to differentiate into specialized cells (Figure 12a). Some of these cells will form capillaries, while others will become osteogenic cells and then osteoblasts. Although they will ultimately be spread out by the formation of bone tissue, early osteoblasts appear in a cluster called an <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2789\">ossification centre<\/a><\/strong>.<\/p>\n<p style=\"text-align: justify\">The osteoblasts secrete <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2790\">osteoid<\/a><\/strong>, uncalcified matrix, which calcifies (hardens) within a few days as mineral salts are deposited on it, thereby entrapping the osteoblasts within. Once entrapped, the osteoblasts become osteocytes (Figure 12b). As osteoblasts transform into osteocytes, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2770\">osteogenic cells<\/a> in the surrounding connective tissue differentiate into new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2766\">osteoblasts<\/a>.<\/p>\n<p style=\"text-align: justify\">Osteoid (unmineralized bone matrix) secreted around the capillaries results in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2775\">trabecular<\/a> matrix, while osteoblasts on the surface of the spongy bone become the periosteum (Figure 12c). The periosteum then creates a protective layer of compact bone superficial to the trabecular bone. The trabecular bone crowds nearby blood vessels, which eventually condense into <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2741\">red marrow<\/a> (Figure 12d).<\/p>\n<p style=\"text-align: justify\">Intramembranous ossification begins <em>in utero <\/em>during fetal development and continues on into adolescence. At birth, the skeleton is not fully ossified. Most joints of the skull, for example, are more mobile in an infant than an adult to allow the skull to deform during passage through the birth canal. The flat bones of the cranium continue to grow throughout childhood, ultimately being separated by narrow immobile joints called sutures.\u00a0 Each clavicle also initially (at about 6 weeks of embryonic age) forms by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2785\">intramembranous ossification<\/a> from two <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2791\">primary ossification centres<\/a> that fuse together <em>in utero<\/em> to form a single bone with cartilage at both ends.\u00a0 This cartilage later ossifies to form the mature clavicles with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2763\">articular cartilage<\/a> on either end (usually in an individual\u2019s early twenties).\u00a0 The last bones to ossify via intramembranous ossification are the flat bones of the face, which reach their adult size at the end of the adolescent growth spurt.\u00a0 The mandible in an infant, for example, consists of two separate bones (left and right), connected by a joint called a symphysis.\u00a0 This mandibular symphysis is fully ossified within the first year of life, permanently fusing the left and right bones to form the mandible.<\/p>\n<figure style=\"width: 1210px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image14-6.png\" alt=\"image\" width=\"1210\" height=\"844\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 12. Intramembranous Ossification.<\/strong> Intramembranous ossification follows four steps. (a) Mesenchymal cells group into clusters, and ossification centers form. (b) Secreted osteoid traps osteoblasts, which then become osteocytes. (c) Trabecular matrix and periosteum form. (d) Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red marrow.<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4c\"><\/a>Endochondral Ossification<\/strong><\/h5>\n<p style=\"text-align: justify\">In <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2792\">endochondral ossification<\/a><\/strong>, bone develops by replacing hyaline cartilage. Cartilage does not become bone, but instead serves as a template to be completely replaced by new bone. Endochondral ossification takes much longer than <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2785\">intramembranous ossification<\/a>. Bones at the base of the skull and long bones form via endochondral ossification.<\/p>\n<p style=\"text-align: justify\">In a long bone, for example, at about 6 to 8 weeks after conception, some of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2306\">mesenchymal<\/a> cells differentiate into chondroblasts (cells that secrete the organic components of cartilage matrix) that form the cartilaginous skeletal precursor of the bones (Figure 13a). Soon after, the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2319\">perichondrium<\/a><\/strong>, a membrane that covers the cartilage, appears (Figure 13b).<\/p>\n<p style=\"text-align: justify\">As more matrix is produced, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2320\">chondrocyte<\/a> in the center of the cartilaginous model grow in size. As the matrix calcifies, nutrients can no longer reach the chondrocytes. This results in their death and the disintegration of the surrounding cartilage. Blood vessels invade the resulting spaces, not only enlarging the cavities but also carrying <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2770\">osteogenic cells<\/a> with them, many of which will become <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2766\">osteoblasts<\/a> (Figure 13c). These enlarging spaces eventually combine to become the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2758\">medullary cavity<\/a> (Figure 13d).<\/p>\n<figure style=\"width: 782px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image15-6.png\" alt=\"image\" width=\"782\" height=\"1041\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 13. Endochondral Ossification.<\/strong> Endochondral ossification follows five steps. (a) Mesenchymal cells differentiate into chondroblasts that secrete cartilage matrix to form a hyaline cartilage model of the future bony skeleton.\u00a0 The perichondrium forms. (b) The cartilage model starts to calcify; chondrocytes begin to die and the cartilage begins to degenerate. (c) Periosteal bud penetrates cartilage of the diaphysis; the primary ossification center develops.\u00a0 A bony collar develops around the diaphysis of the bone.\u00a0 Perichondrium transforms into periosteum.\u00a0 (d) Cartilage continue to grow at ends of the bone. Medullary cavity forms. (e) Periosteal buds penetrate cartilage at epiphyses; secondary ossification centers develop. (f) Cartilage remains at epiphyseal (growth) plate and at joint surface as articular cartilage.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">As the cartilage grows, capillaries penetrate it. This penetration initiates the transformation of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2319\">perichondrium<\/a> into the bone-producing periosteum. Here, the osteoblasts form a periosteal collar of compact bone around the cartilage of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2756\">diaphysis<\/a>. By the second or third month of fetal life, bone cell development and ossification ramps up and creates the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2791\">primary ossification centre<\/a><\/strong>, a region deep in the periosteal collar where ossification begins (Figure 13c).<\/p>\n<p style=\"text-align: justify\">While these deep changes are occurring, chondrocytes and cartilage continue to grow at the ends of the bone (the future <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2757\">epiphyses<\/a>), which increases the bone\u2019s length at the same time bone is replacing cartilage in the diaphyses. By the time the fetal skeleton is fully formed, cartilage only remains at the joint surface as articular cartilage and between the diaphysis and epiphysis as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2760\">epiphyseal plate<\/a>, the latter of which is responsible for the longitudinal growth of bones (Figure 13f). After birth, this same sequence of events (matrix mineralization, death of chondrocytes, invasion of blood vessels from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2764\">periosteum<\/a>, and seeding with osteogenic cells that become osteoblasts) occurs in the epiphyseal regions, and each of these centers of activity is referred to as a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2793\">secondary ossification centre<\/a><\/strong>\u00a0(Figure 13e).<\/p>\n<figure style=\"width: 672px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image16-7.png\" alt=\"image\" width=\"672\" height=\"1045\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 14. Bone Growth in Length.<\/strong> The epiphyseal plate is responsible for longitudinal bone growth.<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4d\"><\/a>How Bones Grow in Length<\/strong><\/h5>\n<p style=\"text-align: justify\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2760\">epiphyseal plate<\/a> is the area of growth in a long bone. It is a layer of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2321\">hyaline cartilage<\/a> where ossification occurs in immature bones. On the epiphyseal side of the epiphyseal plate, cartilage is formed. On the diaphyseal side, cartilage is ossified, and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2756\">diaphysis<\/a> grows in length. The epiphyseal plate is composed of four zones of cells and activity (Figure 14). The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2807\">reserve zone<\/a><\/strong> is the region closest to the epiphyseal end of the plate and contains small chondrocytes within the matrix. These chondrocytes do not participate in bone growth but secure the epiphyseal plate to the osseous tissue of the epiphysis.<\/p>\n<p style=\"text-align: justify\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2808\">proliferative zone<\/a><\/strong> is the next layer toward the diaphysis and contains stacks of slightly larger <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2320\">chondrocytes<\/a>. It makes new chondrocytes (via mitosis) to replace those that die at the diaphyseal end of the plate. Chondrocytes in the next layer, the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2809\">zone of maturation and hypertrophy<\/a><\/strong>, are older and larger than those in the proliferative zone. The more mature cells are situated closer to the diaphyseal end of the plate. The longitudinal growth of bone is a result of cellular division in the proliferative zone and the maturation of cells in the zone of maturation and hypertrophy.<\/p>\n<p style=\"text-align: justify\">Most of the chondrocytes in <strong>the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2810\">zone of calcified matrix<\/a><\/strong>, the zone closest to the diaphysis, are dead because the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2297\">matrix<\/a> around them has calcified. Capillaries and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2766\">osteoblasts<\/a> from the diaphysis penetrate this zone, and the osteoblasts secrete bone tissue on the remaining calcified cartilage.<\/p>\n<p style=\"text-align: justify\">Thus, the zone of calcified matrix connects the epiphyseal plate to the diaphysis. A bone grows in length when osseous tissue is added to the diaphysis.<\/p>\n<p style=\"text-align: justify\">Bones continue to grow in length until early adulthood. The rate of growth is controlled by hormones, which will be discussed later. When the chondrocytes in the epiphyseal plate cease their proliferation and bone replaces the cartilage, longitudinal growth stops. All that remains of the epiphyseal plate is the now fully ossified epiphyseal line (Figure 15).<\/p>\n<figure style=\"width: 787px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image17-5.png\" alt=\"image\" width=\"787\" height=\"624\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 15. Progression from Epiphyseal Plate to Epiphyseal Line.<\/strong> As a bone matures, the epiphyseal plate fully ossifies into an epiphyseal line. (a) Epiphyseal plates are visible in a growing bone. (b) Epiphyseal lines are the remnants of epiphyseal plates in a mature bone.<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"#12A4e\"><\/a>How Bones Grow in Diameter<\/strong><\/h5>\n<p style=\"text-align: justify\">While bones are increasing in length, they are also increasing in diameter; growth in diameter can continue even after longitudinal growth ceases. This is called appositional growth. Osteoclasts resorb old bone that lines the medullary cavity, while osteoblasts, via intramembranous ossification, produce new bone tissue beneath the periosteum. The erosion of old bone along the medullary cavity and the deposition of new bone beneath the periosteum not only increase the diameter of the diaphysis but also increase the diameter of the medullary cavity. This process is called <strong>modeling<\/strong>.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"12A4f\"><\/a>Bone Remodeling<\/strong><\/h5>\n<p style=\"text-align: justify\">The process in which matrix is resorbed on one surface of a bone and deposited on another is known as bone modeling. Modeling primarily takes place during a bone\u2019s growth. However, in adult life, bone undergoes <strong>remodeling<\/strong>, in which resorption of old or damaged bone takes place on the same surface where osteoblasts lay new bone to replace that which is resorbed. Injury, exercise, and other activities lead to remodeling. Those influences are discussed later in the unit, but even without injury or exercise, about 5 to 10 percent of the skeleton is remodeled annually just by destroying old bone and renewing it with fresh bone.<\/p>\n<h2 style=\"text-align: justify\"><strong><a id=\"12A5\"><\/a>Part 5: Fractures<\/strong><\/h2>\n<p style=\"text-align: justify\">A <strong>fracture<\/strong> is a broken bone. It will heal whether or not a physician resets it in its anatomical position. If the bone is not reset correctly, the healing process will keep the bone in its deformed position. Please note that the material in this section (fractures) is not part of the course objectives and therefore not examinable.<\/p>\n<p style=\"text-align: justify\"><strong>Types of Fractures: <\/strong>Fractures are classified by their complexity, location, and other features (Figure 16). Table 3 outlines common types of fractures. Some fractures may be described using more than one term because it may have the features of more than one type (e.g., an open transverse fracture). Of the types pictured in Figure 16 and Table 3, you are only required to understand the details of closed, open, comminuted, and greenstick fractures.<\/p>\n<figure style=\"width: 551px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image18-5.png\" alt=\"image\" width=\"551\" height=\"1048\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 16. Types of Fractures.<\/strong> Compare healthy bone with different types of fractures:(a) closed fracture, (b) open fracture, (c) transverse fracture, (d) spiral fracture, (e) comminuted fracture, (f) impacted fracture, (g) greenstick fracture, and (h) oblique fracture.<\/figcaption><\/figure>\n<table style=\"border-collapse: collapse;width: 100%;height: 141px\">\n<caption>Table 3: Types of Fractures<\/caption>\n<tbody>\n<tr style=\"height: 14px\">\n<th style=\"width: 21.4689%;height: 14px\" scope=\"col\"><strong>Type of fracture<\/strong><\/th>\n<th style=\"width: 78.5311%;height: 14px\" scope=\"col\"><strong>Description<\/strong><\/th>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 21.4689%;height: 14px\">Transverse<\/td>\n<td style=\"width: 78.5311%;height: 14px\">Occurs straight across the long axis of the bone<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 21.4689%;height: 14px\">Oblique<\/td>\n<td style=\"width: 78.5311%;height: 14px\">Occurs at an angle that is not 90 degrees<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 21.4689%;height: 14px\">Spiral<\/td>\n<td style=\"width: 78.5311%;height: 14px\">Bone segments are pulled apart as a result of a twisting motion<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 21.4689%;height: 14px\">Comminuted<\/td>\n<td style=\"width: 78.5311%;height: 14px\">Several breaks result in many small pieces between two large segments<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 21.4689%;height: 14px\">Impacted<\/td>\n<td style=\"width: 78.5311%;height: 14px\">One fragment is driven into the other (usually a result of compression)<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 21.4689%;height: 14px\">Greenstick<\/td>\n<td style=\"width: 78.5311%;height: 14px\">A partial fracture in which only one side of the bone is broken<\/td>\n<\/tr>\n<tr style=\"height: 29px\">\n<td style=\"width: 21.4689%;height: 29px\">Open (compound)<\/td>\n<td style=\"width: 78.5311%;height: 29px\">A fracture in which at least one end of the broken bone tears through the skin; carries a high risk of infection<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<td style=\"width: 21.4689%;height: 14px\">Closed (simple)<\/td>\n<td style=\"width: 78.5311%;height: 14px\">A fracture in which the skin remains intact<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h1 style=\"text-align: justify\"><b>B. Divisions of the Skeletal System<\/b><\/h1>\n<p style=\"text-align: justify\"><span style=\"font-size: 1em\">The skeletal system includes all of the bones, cartilages, and ligaments of the body that support and give shape to the body and body structures. The <\/span><strong style=\"font-size: 1em\">skeleton<\/strong><span style=\"font-size: 1em\"> consists of the bones of the body. For adults, there are 206 bones in the skeleton. Younger individuals have higher numbers of bones because some bones fuse together during childhood and adolescence to form an adult bone.\u00a0 <\/span>The skeleton is subdivided into two major divisions &#8211; the axial skeleton and the appendicular skeleton.<\/p>\n<p style=\"text-align: justify\"><strong>The Axial Skeleton:<\/strong> The skeleton is subdivided into two major divisions\u2014the axial skeleton and appendicular skeleton. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2812\">axial skeleton<\/a><\/strong> forms the vertical, central axis of the body and includes all bones of the head, neck, chest, and back (Figure 17). It serves to protect the brain, spinal cord, heart, and lungs. It also serves as the attachment site for muscles that move the head, neck, and back, and for muscles that act across the shoulder and hip joints to move their corresponding limbs.<\/p>\n<p style=\"text-align: justify\">The axial skeleton of the adult consists of 80 bones, including the <strong>skull<\/strong>, the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2815\">vertebral column<\/a><\/strong>, and the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2816\">thoracic cage<\/a><\/strong>. The skull is formed by 22 bones. Also associated with the head are an additional seven bones, including the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2813\">hyoid bone<\/a><\/strong> and the <strong>ear <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2611\">ossicles<\/a><\/strong>\u00a0(three small bones found in each middle ear). The vertebral column consists of 24 bones, each called a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2818\">vertebra<\/a><\/strong>, plus the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2817\">sacrum<\/a><\/strong> and <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2409\">coccyx<\/a><\/strong>. The thoracic cage includes the 12 pairs of <strong>ribs<\/strong>, and the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2754\">sternum<\/a><\/strong>, the flattened bone of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2357\">anterior<\/a> chest.<\/p>\n<p style=\"text-align: justify\"><strong>The Appendicular Skeleton:<\/strong> The appendicular skeleton includes all bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton (Figure 17). There are 126 bones in the appendicular skeleton of an adult. The bones of the appendicular skeleton are covered later in the unit.<\/p>\n<figure style=\"width: 1028px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" style=\"color: #373d3f;font-weight: bold;font-size: 1em\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image20-5.png\" alt=\"image\" width=\"1028\" height=\"1043\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 17. Axial and Appendicular Skeleton.<\/strong> The axial skeleton supports the head, neck, back, and chest and thus forms the vertical axis of the body. It consists of the skull, vertebral column (including the sacrum and coccyx), and the thoracic cage, formed by the ribs and sternum. The appendicular skeleton is made up of all bones of the upper and lower limbs.<\/figcaption><\/figure>\n<h2><strong><a id=\"12B1\"><\/a>Part 1: The Axial Skeleton<\/strong><\/h2>\n<h5 style=\"text-align: justify\"><strong><a id=\"12B1a\"><\/a>The Skull<\/strong><\/h5>\n<p style=\"text-align: justify\">The <strong>cranium<\/strong> (skull) is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2819\">facial bones<\/a><\/strong> and the <strong>brain case<\/strong>, or cranial vault (Figure 19). The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws. The rounded brain case surrounds and protects the brain and houses the middle and inner ear structures.<\/p>\n<p style=\"text-align: justify\">In the adult, the skull consists of 22 individual bones, 21 of which are immobile and united into a single unit. The 22nd bone is the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2820\">mandible<\/a><\/strong> (lower jaw), which is the only moveable bone of the skull.<\/p>\n<p style=\"text-align: justify\"><strong>Development of the Skull:<\/strong> As the brain case bones grow in the fetal skull, they remain separated from each other by large areas of dense connective tissue, each of which is called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2821\">fontanelle<\/a> (Figure 18). The fontanelles are the soft spots on an infant\u2019s head. They are important during birth because these areas allow the skull to change shape as it squeezes through the birth canal. After birth, the fontanelles allow for continued growth and expansion of the skull as the brain enlarges. The largest fontanelle is located on the anterior head, at the junction of the frontal and parietal bones. The fontanelles decrease in size and disappear by age 2. However, the skull bones remained separated from each other at the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2822\">sutures<\/a>, which contain dense fibrous connective tissue that unites the adjacent bones. The connective tissue of the sutures allows for continued growth of the skull bones as the brain enlarges during childhood growth. This structure also means that, although the size of the cranium increases from birth to adulthood, proportionately it does so less than other parts of the skeleton; the relative size of the cranium in proportion to the rest of the body therefore decreases with age from birth to adulthood.<\/p>\n<figure style=\"width: 1671px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image21-5.png\" alt=\"image\" width=\"1671\" height=\"557\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 18. Newborn Skull.<\/strong> The bones of the newborn skull are not fully ossified and are separated by large areas called fontanelles, which are filled with fibrous connective tissue. The fontanelles allow for continued growth of the skull after birth. At the time of birth, the facial bones are small and underdeveloped, and the mastoid process has not yet formed.<\/figcaption><\/figure>\n<figure style=\"width: 1256px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" style=\"color: #373d3f;font-weight: bold;font-size: 1em\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image22-5.png\" alt=\"image\" width=\"1256\" height=\"1036\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 19. Parts of the Skull.<\/strong> The skull consists of the rounded brain case that houses the brain and the facial bones that form the upper and lower jaws, nose, orbits, and other facial structures.<\/figcaption><\/figure>\n<figure style=\"width: 1234px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" style=\"color: #373d3f;font-weight: bold;font-size: 1em\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image23-4.png\" alt=\"image\" width=\"1234\" height=\"1041\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 20. Anterior View of Skull.<\/strong> An anterior view of the skull shows the bones that form the forehead, orbits (eye sockets), nasal cavity, nasal septum, and upper and lower jaws.<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Bones of the Brain Case:<\/strong> The brain case contains and protects the brain (Figure 19). The interior space that is almost completely occupied by the brain is called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2391\">cranial cavity<\/a><\/strong>.<\/p>\n<p style=\"text-align: justify\">The brain case consists of eight bones (Figures 20 &amp; 21). These include the paired <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2823\">parietal<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2824\">temporal<\/a> bones, plus the unpaired <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2825\">frontal<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2826\">occipital<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2827\">sphenoid<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2828\">ethmoid<\/a> bones. For our purposes, we will not be specifying the details of the sphenoid and ethmoid bones.<\/p>\n<p style=\"text-align: justify\">1. Parietal Bone: The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2823\">parietal bone<\/a><\/strong> forms most of the upper lateral side of the skull (Figures 21 &amp; 22). These are paired bones, with the right and left parietal bones joining together at the top of the skull. Each parietal bone is also bounded anteriorly by the frontal bone, inferiorly by the temporal bone, and posteriorly by the occipital bone.<\/p>\n<p style=\"text-align: justify\">2. Temporal Bone: The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2620\">temporal bone<\/a><\/strong> forms the lower lateral side of the skull (Figure 21). Common wisdom has it that the temporal bone (temporal = \u201ctime\u201d) is so named because this area of the head (the temple) is where hair typically first turns gray, indicating the passage of time.<\/p>\n<figure style=\"width: 1514px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image24-4.png\" alt=\"image\" width=\"1514\" height=\"1037\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 21. Lateral View of Skull.<\/strong> The lateral skull shows the large rounded brain case, zygomatic arch, and the upper and lower jaws. The zygomatic arch is formed jointly by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. The shallow space above the zygomatic arch is the temporal fossa. The space inferior to the zygomatic arch and deep to the posterior mandible is the infratemporal fossa.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">3. Frontal Bone: The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2825\">frontal bone<\/a> is the single bone that forms the forehead (Figure 20).<\/p>\n<p style=\"text-align: justify\">4. Occipital Bone: The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2826\">occipital bone<\/a><\/strong> is the single bone that forms the posterior skull and posterior base of the cranial cavity (Figures 21 &amp; 22). On its outside surface, at the posterior midline, is a small protrusion called the <strong>external occipital protuberance<\/strong>, which serves as an attachment site for a ligament of the posterior neck.<\/p>\n<figure style=\"width: 809px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image25-4.png\" alt=\"image\" width=\"809\" height=\"628\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 22. Posterior View of Skull.<\/strong> This view of the posterior skull shows attachment sites for muscles and joints that support the skull.<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Facial Bones of the Skull: <\/strong>The facial bones of the skull form the upper and lower jaws, the nose, nasal cavity and nasal septum, and the orbit. The facial bones include 14 bones, with six paired bones and two unpaired bones (Figures 20 &amp; 21). We will focus on the maxillary bones and the mandible bone.<\/p>\n<p style=\"text-align: justify\">1. Maxillary Bone: The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2832\">maxillary bone<\/a><\/strong>, often referred to simply as the maxilla (plural = maxillae), is one of a pair that together form the upper jaw, much of the hard palate, the medial floor of the orbit, and the lateral base of the nose (Figures 20 &amp; 21).<\/p>\n<p style=\"text-align: justify\">2. Mandible: The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2820\">mandible<\/a><\/strong> forms the lower jaw and is the only moveable bone of the skull. At the time of birth, the mandible consists of paired right and left bones, but these fuse together during the first year to form the single U-shaped mandible of the adult skull (Figures 20 &amp; 21).<\/p>\n<p style=\"text-align: justify\"><strong>The Bones of the Middle Ear:<\/strong> Three small bones (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2611\">ossicles<\/a>) are found on either side of the head in the middle ear. These are the malleus, incus, and stapes, and they function in transferring the vibrations from the eardrum (tympanic membrane) to the inner ear.<\/p>\n<p style=\"text-align: justify\"><strong>The Hyoid Bone:<\/strong> The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2813\">hyoid bone<\/a> is an independent bone that does not contact any other bone and thus is not part of the skull (Figure 23). It is a small U-shaped bone located in the upper neck near the level of the inferior mandible, with the tips of the \u201cU\u201d pointing posteriorly. The hyoid serves as the base for the tongue above and is attached to the larynx below and the pharynx posteriorly. The hyoid is held in position by a series of small muscles that attach to it either from above or below. These muscles act to move the hyoid up\/down or forward\/back. Movements of the hyoid are coordinated with movements of the tongue, larynx, and pharynx during swallowing and speaking.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"12B1b\"><\/a>The Vertebral Column<\/strong><\/h5>\n<p style=\"text-align: justify\">The vertebral column is also known as the spinal column or spine (Figure 24). It consists of a sequence of vertebrae (singular = vertebra), each of which is separated and united by an <strong>intervertebral disc<\/strong>. Together, the vertebrae and intervertebral discs form the vertebral column. It is a flexible column that supports the head, neck, and body and allows for their movements. It also protects the spinal cord, which passes down the back through openings in the vertebra.<\/p>\n<p style=\"text-align: justify\"><strong>Regions of the Vertebral Column<\/strong>: The vertebral column originally develops as a series of 33 vertebrae, but this number is eventually reduced to 24 vertebrae, plus the sacrum and coccyx. The vertebral column is subdivided into five regions, with the vertebrae in each area named for that region and numbered in descending order. In the neck, there are seven cervical vertebrae, each designated with the letter \u201cC\u201d followed by its number. Superiorly, the C1 vertebra articulates (forms a joint) with the occipital condyles of the skull. Inferiorly, C1 articulates with the C2 vertebra, and so on. Below these are the 12 thoracic vertebrae, designated T1\u2013T12. The lower back contains the L1\u2013L5 lumbar vertebrae. The single sacrum, which is also part of the pelvis, is formed by the fusion of five sacral vertebrae. Similarly, the coccyx, or tailbone, results from the fusion of four small coccygeal vertebrae. However, the sacral and coccygeal fusions do not start until age 20 and are not completed until middle age.<\/p>\n<figure style=\"width: 542px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image26-4.png\" alt=\"image\" width=\"542\" height=\"846\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 23. Hyoid Bone.<\/strong> The hyoid bone is located in the upper neck and does not join with any other bone. It provides attachments for muscles that act on the tongue, larynx, and pharynx.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong>Curvatures of the Vertebral Column:<\/strong> The adult vertebral column does not form a straight line, but instead has four curvatures along its length (see Figure 24). These curves increase the vertebral column\u2019s strength, flexibility, and ability to absorb shock.<\/p>\n<p style=\"text-align: justify\">During fetal development, the body is flexed anteriorly into the fetal position, giving the entire vertebral column a single curvature that is concave anteriorly. In the adult, this fetal curvature is retained in two regions of the vertebral column as the <strong>thoracic curve<\/strong>, which involves the thoracic vertebrae, and the <strong>sacrococcygeal curve<\/strong>, formed by the sacrum and coccyx.<\/p>\n<figure style=\"width: 817px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image27-4.png\" alt=\"image\" width=\"817\" height=\"779\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 24. Vertebral Column.<\/strong> The adult vertebral column consists of 24 vertebrae, plus the sacrum and coccyx. The vertebrae are divided into three regions: cervical C1\u2013C7 vertebrae, thoracic T1\u2013T12 vertebrae, and lumbar L1\u2013L5 vertebrae. The vertebral column is curved, with two primary curvatures (thoracic and sacrococcygeal curves) and two secondary curvatures (cervical and lumbar curves).<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong>General Structure of a Vertebra:<\/strong> Within the different regions of the vertebral column, vertebrae vary in size and shape, but they all follow a similar structural pattern. A typical vertebra will consist of a body, a vertebral arch, and seven processes (Figure 25).<\/p>\n<p style=\"text-align: justify\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2843\">body<\/a><\/strong> is the anterior portion of each vertebra and is the part that supports the body weight. Because of this, the vertebral bodies progressively increase in size and thickness going down the vertebral column. The bodies of adjacent vertebrae are separated and strongly united by an intervertebral disc.<\/p>\n<p style=\"text-align: justify\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2840\">vertebral arch<\/a><\/strong> forms the posterior portion of each vertebra.<\/p>\n<p style=\"text-align: justify\">The large opening between the vertebral arch and body is the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2842\">vertebral foramen<\/a><\/strong>, which contains the spinal cord. In the intact vertebral column, the vertebral foramina of all of the vertebrae align to form the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2841\">vertebral (spinal) canal<\/a><\/strong>, which serves as the bony protection and passageway for the spinal cord down the back. When the vertebrae are aligned together in the vertebral column, notches in the margins of the pedicles of adjacent vertebrae together form an <strong>intervertebral foramen<\/strong>, the opening through which a spinal nerve exits from the vertebral column (Figure 26).<\/p>\n<figure style=\"width: 1091px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image28-4.png\" alt=\"image\" width=\"1091\" height=\"472\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 25. Parts of a Typical Vertebra.<\/strong> A typical vertebra consists of a body and a vertebral arch. The arch is formed by the paired pedicles and paired laminae. Arising from the vertebral arch are the transverse, spinous, superior articular, and inferior articular processes. The vertebral foramen provides for passage of the spinal cord. Each spinal nerve exits through an intervertebral foramen, located between adjacent vertebrae. Intervertebral discs unite the bodies of adjacent vertebra<\/figcaption><\/figure>\n<p style=\"text-align: justify\">Seven processes arise from the vertebral arch. Each paired <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2858\"><strong>transverse process<\/strong><\/a> projects laterally and arises from the junction point between the pedicle and lamina. The single <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2844\">spinous process<\/a><\/strong> (vertebral spine) projects posteriorly at the midline of the back. The vertebral spines can easily be felt as a series of bumps just under the skin down the middle of the back. The transverse and spinous processes serve as important muscle attachment sites. A <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2845\">superior articular process<\/a><\/strong> extends or faces upward, and an <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2846\">inferior articular process<\/a><\/strong> faces or projects downward on each side of a vertebrae. The paired superior articular processes of one vertebra join with the corresponding paired inferior articular processes from the next higher vertebra. These junctions form slightly moveable joints between the adjacent vertebrae. The shape and orientation of the articular processes vary in different regions of the vertebral column and play a major role in determining the type and range of motion available in each region.<\/p>\n<p style=\"text-align: justify\"><strong>Regional Modifications of Vertebrae:<\/strong> In addition to the general characteristics of a typical vertebra described above, vertebrae also display characteristic size and structural features that vary between the different vertebral column regions. Thus, cervical vertebrae are smaller than lumbar vertebrae due to differences in the proportion of body weight that each will support. Thoracic vertebrae have sites for rib attachment, and the vertebrae that give rise to the sacrum and coccyx have fused together into single bones. We will focus on the anatomically distinct natures of the first two cervical vertebrae, the atlas and the axis.<\/p>\n<figure style=\"width: 997px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image29-4.png\" alt=\"image\" width=\"997\" height=\"470\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 26. Intervertebral Disc.<\/strong> The bodies of adjacent vertebrae are separated and united by an intervertebral disc, which provides padding and allows for movements between adjacent vertebrae. The disc consists of a fibrous outer layer called the anulus fibrosus and a gel-like center called the nucleus pulposus. The intervertebral foramen is the opening formed between adjacent vertebrae for the exit of a spinal nerve.<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Cervical Vertebrae: <\/strong>Typical <strong>cervical vertebrae<\/strong>, such as C4 or C5, have several characteristic features that differentiate them from thoracic or lumbar vertebrae (Figure 27). Cervical vertebrae have a small body, reflecting the fact that they carry the least amount of body weight. Cervical vertebrae usually have a bifid (Y-shaped) <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2844\">spinous process<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2858\">transverse processes<\/a> of the cervical vertebrae are sharply curved (U-shaped) to allow for passage of the cervical spinal nerves. Each transverse process also has an opening called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2847\">transverse foramen<\/a><\/strong>.<\/p>\n<p style=\"text-align: justify\">The first and second cervical vertebrae are further modified, giving each a distinctive appearance. The first cervical (C1) vertebra is also called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2848\">atlas<\/a><\/strong>, because this is the vertebra that supports the skull on top of the vertebral column (in Greek mythology, Atlas was the god who supported the heavens on his shoulders). The C1 vertebra does not have a body or spinous process. Instead, it is ring-shaped, consisting of an <strong>anterior arch<\/strong> and a <strong>posterior arch<\/strong>. The transverse processes of the atlas are longer and extend more laterally than do the transverse processes of any other cervical vertebrae. The superior articular processes face upward and are deeply curved for articulation with the occipital condyles on the base of the skull. The inferior articular processes are flat and face downward to join with the superior articular processes of the C2 vertebra.<\/p>\n<p style=\"text-align: justify\">The second cervical (C2) vertebra is called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2849\">axis<\/a><\/strong>, because it serves as the axis for rotation when turning the head toward the right or left. The axis resembles typical cervical vertebrae in most respects but is easily distinguished by the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2850\">dens<\/a><\/strong> (odontoid process), a bony projection that extends upward from the vertebral body. The dens joins with the inner aspect of the anterior arch of the atlas, where it is held in place by transverse ligament.<\/p>\n<figure style=\"width: 915px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image30-4.png\" alt=\"image\" width=\"915\" height=\"1045\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 27. Cervical Vertebrae.<\/strong> A typical cervical vertebra has a small body, a bifid spinous process, transverse processes that have a transverse foramen and are curved for spinal nerve passage. The atlas (C1 vertebra) does not have a body or spinous process. It consists of an anterior and a posterior arch and elongated transverse processes. The axis (C2 vertebra) has the upward projecting dens, which articulates with the anterior arch of the atlas.<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"12B1c\"><\/a>The Thoracic Cage<\/strong><\/h5>\n<p style=\"text-align: justify\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2816\">thoracic cage<\/a> (rib cage) forms the thorax (chest) portion of the body. It consists of the 12 pairs of ribs with their costal cartilages and the sternum (Figure 28). The ribs are anchored posteriorly to the 12 thoracic vertebrae (T1\u2013T12). The thoracic cage protects the heart and lungs.<\/p>\n<p style=\"text-align: justify\"><strong>Sternum: <\/strong>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2754\">sternum<\/a> is the elongated bony structure that anchors the anterior thoracic cage. It consists of three parts: the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2851\">manubrium<\/a>, body, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2852\">xiphoid process<\/a>.<\/p>\n<figure style=\"width: 1144px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image31-4.png\" alt=\"image\" width=\"1144\" height=\"674\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 28. Thoracic Cage.<\/strong> The thoracic cage is formed by the (a) sternum and (b) 12 pairs of ribs with their costal cartilages. The ribs are anchored posteriorly to the 12 thoracic vertebrae. The sternum consists of the manubrium, body, and xiphoid process. The ribs are classified as true ribs (1\u20137) and false ribs (8\u201312). The last two pairs of false ribs are also known as floating ribs (11\u201312)<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Ribs: <\/strong>Each rib is a curved, flattened bone that contributes to the wall of the thorax. The ribs articulate posteriorly with the T1\u2013T12 thoracic vertebrae, and most attach anteriorly via their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2853\">costal cartilages<\/a> to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2754\">sternum<\/a>. There are 12 pairs of ribs. The ribs are numbered 1\u201312 in accordance with the thoracic vertebrae.<\/p>\n<p style=\"text-align: justify\">The bony ribs do not extend anteriorly completely around to the sternum. Instead, each rib ends in a costal cartilage. These cartilages are made of hyaline cartilage and can extend for several inches. Most ribs are then attached, either directly or indirectly, to the sternum via their costal cartilage (Figure 28). The ribs are classified into three groups based on their relationship to the sternum.<\/p>\n<p style=\"text-align: justify\">Ribs 1\u20137 are classified as <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2854\">true ribs<\/a><\/strong> (vertebrosternal ribs). The costal cartilage from each of these ribs attaches directly to the sternum. Ribs 8\u201312 are called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2855\">false ribs<\/a><\/strong> (vertebrochondral ribs). The costal cartilages from these ribs do not attach directly to the sternum. For ribs 8\u201310, the costal cartilages are attached to the cartilage of the next higher rib. Thus, the cartilage of rib 10 attaches to the cartilage of rib 9, rib 9 then attaches to rib 8, and rib 8 is attached to rib 7. The last two false ribs (11\u201312) are also called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2856\">floating ribs<\/a><\/strong> (vertebral ribs). These are short ribs that do not attach to the sternum at all. Instead, their small costal cartilages terminate within the musculature of the lateral abdominal wall.<\/p>\n<h2 style=\"text-align: justify\"><strong><a id=\"12B2\"><\/a>Part 2. The Appendicular Skeleton<\/strong><\/h2>\n<p style=\"text-align: justify\">Attached to the axial skeleton are the limbs, whose 126 bones constitute the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2860\">appendicular skeleton<\/a> (Figure 29) These bones are divided into two groups: the bones that are located within the limbs themselves, and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2859\">girdle<\/a> bones that attach the limbs to the axial skeleton. The bones of the shoulder region form the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2861\">pectoral girdle<\/a>, which anchors the upper limb to the thoracic cage of the axial skeleton. The lower limb is attached to the vertebral column by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2862\">pelvic girdle<\/a>.<\/p>\n<p style=\"text-align: justify\">Because of our upright stance, different functional demands are placed upon the upper and lower limbs. Thus, the bones of the lower limbs are adapted for weight-bearing support and stability, as well as for body locomotion via walking or running. In contrast, our upper limbs are not required for these functions. Instead, our upper limbs are highly mobile and can be utilized for a wide variety of activities. The large range of upper limb movements, coupled with the ability to easily manipulate objects with our hands and opposable thumbs, has allowed humans to construct the modern world in which we live.<\/p>\n<h5 style=\"text-align: justify\"><strong><a id=\"12B2a\"><\/a>The Pectoral Girdle<\/strong><\/h5>\n<p style=\"text-align: justify\">The bones that attach each upper limb to the axial skeleton form the pectoral girdle (shoulder girdle). This consists of two bones, the scapula and clavicle (Figure 30).<\/p>\n<p style=\"text-align: justify\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2786\">clavicle<\/a><\/strong> (collarbone) is an S-shaped bone located on the anterior side of the shoulder. It is attached on its <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2362\">medial<\/a> end to the sternum of the thoracic cage, which is part of the axial skeleton. The lateral end of the clavicle articulates (joins) with the scapula just above the shoulder joint. You can easily palpate, or feel with your fingers, the entire length of your clavicle.<\/p>\n<p style=\"text-align: justify\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2755\">scapula<\/a><\/strong> (shoulder blade) lies on the posterior aspect of the shoulder. It is supported by the clavicle, which also articulates with the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2746\">humerus<\/a> (upper arm bone) to form the shoulder joint. The scapula is a flat, triangular-shaped bone with a prominent ridge running across its <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2358\">posterior<\/a> surface. This ridge extends out laterally, where it forms the bony tip of the shoulder and joins with the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2361\">lateral<\/a> end of the clavicle. By following along the clavicle, you can palpate out to the bony tip of the shoulder, and from there, you can move back across your posterior shoulder to follow the ridge of the scapula. Move your shoulder around and feel how the clavicle and scapula move together as a unit. Both of these bones serve as important attachment sites for muscles that aid with movements of the shoulder and arm. (Figures 30 &amp; 31)<\/p>\n<figure style=\"width: 1028px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image32-4.png\" alt=\"image\" width=\"1028\" height=\"1047\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 29. Axial and Appendicular Skeletons.<\/strong> The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and thoracic cage. The appendicular skeleton consists of the pectoral and pelvic girdles, the limb bones, and the bones of the hands and feet.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">The right and left pectoral girdles are not joined to each other, allowing each to operate independently. In addition, the clavicle of each pectoral girdle is anchored to the axial skeleton by a single, highly mobile joint. This allows for the extensive mobility of the entire pectoral girdle, which in turn enhances movements of the shoulder and upper limb.<\/p>\n<figure style=\"width: 760px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image33-4.png\" alt=\"image\" width=\"760\" height=\"1045\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 30. Pectoral Girdle.<\/strong> The pectoral girdle consists of the clavicle and the scapula, which serve to attach the upper limb to the sternum of the axial skeleton.<\/figcaption><\/figure>\n<figure style=\"width: 971px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image34-4.png\" alt=\"image\" width=\"971\" height=\"640\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 31. Scapula.<\/strong> The isolated scapula is shown here from its anterior (deep) side and its posterior (superficial) side.<\/figcaption><\/figure>\n<h5 style=\"text-align: justify\"><strong><a id=\"12B2b\"><\/a>Bones of the Upper Limb<\/strong><\/h5>\n<p style=\"text-align: justify\">The upper limb is divided into three regions. These consist of the <strong>arm<\/strong>, located between the shoulder and elbow joints; the <strong>forearm<\/strong>, which is between the elbow and wrist joints; and the <strong>hand<\/strong>, which is located distal to the wrist. There are 30 bones in each upper limb. The <strong>humerus<\/strong> is the single bone of the upper arm, and the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2745\">ulna<\/a><\/strong> (medially) and the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2747\">radius<\/a><\/strong> (laterally) are the paired bones of the forearm. The base of the hand contains eight bones, each called a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2752\">carpal<\/a> bone<\/strong>, and the palm of the hand is formed by five bones, each called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2744\">metacarpal<\/a> bone. The fingers and thumb contain a total of 14 bones, each of which is a <strong>phalanx bone of the hand<\/strong>. (Figure 29)<\/p>\n<p style=\"text-align: justify\"><strong>Humerus:<\/strong> The humerus is the single bone of the upper arm region (Figure 32). At its proximal end is the head of the humerus. This is the large, round, smooth region that faces medially. The head articulates with the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2863\">glenoid cavity<\/a> of the scapula to form the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2864\">glenohumeral<\/a> (shoulder) joint. Distally, the humerus becomes flattened and has two articulation areas, which join the ulna and radius bones of the forearm to form the <strong>elbow joint<\/strong><\/p>\n<p style=\"text-align: justify\"><strong>Ulna:<\/strong> The ulna is the medial bone of the forearm. It runs parallel to the radius, which is the lateral bone of the forearm (Figure 33). The proximal end of the ulna articulates with the humerus as part of the elbow joint.<\/p>\n<p style=\"text-align: justify\"><strong>Radius:<\/strong> The radius runs parallel to the ulna, on the lateral (thumb) side of the forearm (Figure 33). The head of the radius is a disc-shaped structure that forms the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2373\">proximal<\/a> end. The distal end of the radius has a smooth surface for articulation with two carpal bones to form <strong>the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2865\">radiocarpal joint<\/a><\/strong> or wrist joint (Figure 34 &amp; 35).<\/p>\n<figure style=\"width: 673px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image35-5.png\" alt=\"image\" width=\"673\" height=\"847\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 32. Humerus and Elbow Joint.<\/strong> The humerus is the single bone of the upper arm region. It articulates with the radius and ulna bones of the forearm to form the elbow joint.<\/figcaption><\/figure>\n<p><strong>Carpal Bones:<\/strong> The wrist and base of the hand are formed by a series of eight small carpal bones (Figure 34). The carpal bones are arranged in two rows, forming a proximal row of four carpal bones and a distal row of four carpal bones.<\/p>\n<figure style=\"width: 636px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image36-4.png\" alt=\"image\" width=\"636\" height=\"824\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 33. Ulna and Radius.<\/strong> The ulna is located on the medial side of the forearm, and the radius is on the lateral side. These bones are attached to each other by an interosseous membrane.<\/figcaption><\/figure>\n<figure style=\"width: 976px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image37-4.png\" alt=\"image\" width=\"976\" height=\"783\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 34. Bones of the Wrist and Hand.<\/strong> The eight carpal bones form the base of the hand. These are arranged into proximal and distal rows of four bones each. The metacarpal bones form the palm of the hand. The thumb and fingers consist of the phalanx bones.<\/figcaption><\/figure>\n<figure style=\"width: 968px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image38-5.png\" alt=\"image\" width=\"968\" height=\"585\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 35. Bones of the Hand.<\/strong> This radiograph shows the position of the bones within the hand. Note the carpal bones that form the base of the hand. (credit: modification of work by Trace Meek)<\/figcaption><\/figure>\n<p style=\"text-align: justify\">The carpal bones form the base of the hand. This can be seen in the radiograph (X-ray image) of the hand that shows the relationships of the hand bones to the skin creases of the hand (Figure35).<\/p>\n<p style=\"text-align: justify\"><strong>Metacarpal Bones:<\/strong> The palm of the hand contains five elongated metacarpal bones. These bones lie between the carpal bones of the wrist and the bones of the fingers and thumb (Figure 34). The proximal end of each metacarpal bone articulates with one of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2374\">distal<\/a> carpal bones. Each of these articulations is a carpometacarpal joint (Figure 35). The expanded distal end of each metacarpal bone articulates at the metacarpophalangeal joint with the proximal phalanx bone of the thumb or one of the fingers. The distal end also forms the knuckles of the hand, at the base of the fingers. The metacarpal bones are numbered 1\u20135, beginning at the thumb.<\/p>\n<p style=\"text-align: justify\"><strong>Phalanx Bones:<\/strong> The fingers and thumb contain 14 bones, each of which is called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2750\">phalanx<\/a> bone (plural = phalanges), named after the ancient Greek phalanx (a rectangular block of soldiers). The thumb (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2405\">pollex<\/a>) is digit number 1 and has two phalanges, a proximal phalanx, and a distal phalanx bone (Figure 34). Digits 2 (index finger) through 5 (little finger) have three phalanges each, called the proximal, middle, and distal phalanx bones. An <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2866\">interphalangeal joint<\/a><\/strong> is one of the articulations between adjacent phalanges of the digits (Figure 35).<\/p>\n<p style=\"text-align: justify\"><strong>Part 3: The Pelvic Girdle and Pelvis<\/strong><\/p>\n<p style=\"text-align: justify\">The <strong>pelvic girdle<\/strong> (hip girdle) is formed by a single bone, the <strong>hip bone<\/strong> or <strong>coxal bone<\/strong> (coxal = \u201chip\u201d), which serves as the attachment point for each lower limb. Each hip bone, in turn, is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left hip bones also converge anteriorly to attach to each other. The bony <strong>pelvis<\/strong> is the entire structure formed by the two hip bones, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2817\">sacrum<\/a>, and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2409\">coccyx<\/a> that is attached inferiorly to the sacrum (Figure 36).<\/p>\n<figure style=\"width: 1151px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image39-4.png\" alt=\"image\" width=\"1151\" height=\"782\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 36. Pelvis.<\/strong> The pelvic girdle is formed by a single hip bone. The hip bone attaches the lower limb to the axial skeleton through its articulation with the sacrum. The right and left hip bones, plus the sacrum and the coccyx, together form the pelvis.<\/figcaption><\/figure>\n<p style=\"text-align: justify\">Unlike the bones of the pectoral girdle, which are highly mobile to enhance the range of upper limb movements, the bones of the pelvis are strongly united to each other to form a largely immobile, weight-bearing structure. This is important for stability because it enables the weight of the body to be easily transferred laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb whenever the other limb is not bearing weight. Thus, the immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs.<\/p>\n<p style=\"text-align: justify\"><strong>Hip Bone:<\/strong> The hip bone, or coxal bone, forms the pelvic girdle portion of the pelvis. The paired hip bones are the large, curved bones that form the lateral and anterior aspects of the pelvis. Each adult hip bone is formed by three separate bones that fuse together during the late teenage years. These bony components are the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2867\">ilium<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2868\">ischium<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2869\">pubis<\/a> (Figure 37). These names are retained and used to define the three regions of the adult hip bone.<\/p>\n<p style=\"text-align: justify\">The<strong> ilium<\/strong> is the fan-like, superior region that forms the largest part of the hip bone. It is firmly united to the sacrum at the largely immobile <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2870\">sacroiliac joint<\/a><\/strong> (Figure 36). The <strong>ischium<\/strong> forms the posteroinferior region of each hip bone. It supports the body when sitting. The <strong>pubis<\/strong> forms the anterior portion of the hip bone. The pubis curves medially, where it joins to the pubis of the opposite hip bone at a specialized joint called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2871\">pubic symphysis<\/a><\/strong>.<\/p>\n<figure style=\"width: 973px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image40-4.png\" alt=\"image\" width=\"973\" height=\"698\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 37. The Hip Bone.<\/strong> The adult hip bone consists of three regions. The ilium forms the large, fan-shaped superior portion, the ischium forms the posteroinferior portion, and the pubis forms the anteromedial portion.<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Pelvis:<\/strong> The pelvis consists of four bones: the right and left hip bones, the sacrum, and the coccyx (Figure 36). The pelvis has several important functions. Its primary role is to support the weight of the upper body when sitting and to transfer this weight to the lower limbs when standing. It serves as an attachment point for trunk and lower limb muscles, and also protects the internal pelvic organs.<\/p>\n<figure style=\"width: 953px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image41-4.png\" alt=\"image\" width=\"953\" height=\"447\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 38. Male and Female Pelves.<\/strong> The female pelvis is adapted for childbirth and is broader, with a larger subpubic angle, a rounder pelvic brim, and a wider and more shallow lesser pelvic cavity than the male pelvis.<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Comparison of the Female and Male Pelvis:<\/strong> The differences between the adult female and male pelvis relate to function and body size. In general, the bones of the male pelvis are thicker and heavier, adapted for support of the male\u2019s heavier physical build and stronger muscles; this average size difference is generally true of other bones of the skeleton as well. The pelvis does show more robust differences between males and females due to its functional relationship to bipedal movement (requiring a relatively narrow pelvis) and birth of infants with large brains (requiring a relatively broad pelvis). Because the female pelvis is adapted for childbirth, it is wider than the male pelvis, as evidenced by the distance between the anterior superior iliac spines (Figure 38). The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2872\">ischial tuberosities<\/a> of females are also farther apart, which increases the size of the pelvic outlet. Because of this increased pelvic width, the subpubic angle is larger in females (greater than 80 degrees) than it is in males (less than 70 degrees). The female sacrum is wider, shorter, and less curved, and the sacral promontory projects less into the pelvic cavity, thus giving the female pelvic inlet (pelvic brim) a more rounded or oval shape compared to males. The pelvic cavity of females is also wider and shallower than the narrower, deeper, and tapering lesser pelvis of males. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2873\">greater sciatic notch<\/a> of the male hip bone is narrower and deeper than the broader notch of females. Because of the obvious differences between female and male hip bones, this is the one bone of the body that allows for the most accurate sex determination. Table 4 provides an overview of the general differences between the female and male pelvis.<\/p>\n<table style=\"border-collapse: collapse;width: 100%;height: 85px\">\n<caption>Table 4: Overview of Differences Between Average Female and Male Pelves<\/caption>\n<tbody>\n<tr style=\"height: 14px\">\n<td style=\"width: 33.3333%;height: 14px\"><\/td>\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\"><strong>Female pelvis<\/strong><\/th>\n<th style=\"width: 33.3333%;height: 14px\" scope=\"col\"><strong>Male pelvis<\/strong><\/th>\n<\/tr>\n<tr style=\"height: 29px\">\n<th style=\"width: 33.3333%;height: 29px\" scope=\"row\"><strong>Pelvic weight<\/strong><\/th>\n<td style=\"width: 33.3333%;height: 29px\">Bones are lighter and thinner<\/td>\n<td style=\"width: 33.3333%;height: 29px\">Bones are thicker and heavier<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<th style=\"width: 33.3333%;height: 14px\" scope=\"row\"><strong>Pelvis inlet shape<\/strong><\/th>\n<td style=\"width: 33.3333%;height: 14px\">Round or oval<\/td>\n<td style=\"width: 33.3333%;height: 14px\">Heart-shaped<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<th style=\"width: 33.3333%;height: 14px\" scope=\"row\"><strong>Lesser pelvic cavity shape<\/strong><\/th>\n<td style=\"width: 33.3333%;height: 14px\">Shorter and wider<\/td>\n<td style=\"width: 33.3333%;height: 14px\">Longer and narrower<\/td>\n<\/tr>\n<tr style=\"height: 14px\">\n<th style=\"width: 33.3333%;height: 14px\" scope=\"row\"><strong>Subpubic angle<\/strong><\/th>\n<td style=\"width: 33.3333%;height: 14px\">Greater than 80 degrees<\/td>\n<td style=\"width: 33.3333%;height: 14px\">Less than 70 degrees<\/td>\n<\/tr>\n<tr>\n<th style=\"width: 33.3333%\" scope=\"row\"><strong>Pelvic outlet shape<\/strong><\/th>\n<td style=\"width: 33.3333%\">Rounded and larger<\/td>\n<td style=\"width: 33.3333%\">Smaller<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p style=\"text-align: justify\"><strong>Part 4: Bones of the Lower Limb<\/strong><\/p>\n<p style=\"text-align: justify\">Like the upper limb, the lower limb is divided into three regions. The <strong>thigh<\/strong> is that portion of the lower limb located between the hip joint and knee joint. The <strong>leg<\/strong> is specifically the region between the knee joint and the ankle joint. Distal to the ankle is the <strong>foot<\/strong>. The lower limb contains 30 bones. These are the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2379\">femur<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2408\">patella<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2748\">tibia<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2749\">fibula<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2753\">tarsal<\/a> bones, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2743\">metatarsal<\/a> bones, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2750\">phalanges<\/a> (Figure 29). The <strong>femur<\/strong> is the single bone of the thigh. The <strong>patella<\/strong> is the kneecap and articulates with the distal femur. The <strong>tibia<\/strong> is the larger, weight-bearing bone located on the medial side of the leg, and the <strong>fibula <\/strong>is the thin bone of the lateral leg. The bones of the foot are divided into three groups. The posterior portion of the foot is formed by a group of seven bones, each of which is known as a <strong>tarsal bone<\/strong>, whereas the mid-foot contains five elongated bones, each of which is a <strong>metatarsal bone<\/strong>. The toes contain 14 small bones, each of which is a <strong>phalanx bone of the foot<\/strong>.<\/p>\n<p style=\"text-align: justify\"><strong>Femur:<\/strong> The femur, or thigh bone, is the single bone of the thigh region (Figure 39). It is the longest and strongest bone of the body, and accounts for approximately one-quarter of a person\u2019s total height. The rounded, proximal end is the head of the femur, which articulates with the acetabulum of the hip bone to form the <strong>hip joint<\/strong>.<\/p>\n<p style=\"text-align: justify\"><strong>Patella:<\/strong> The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2408\">patella<\/a> (kneecap) is the largest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2874\">sesamoid<\/a> bone of the body (see Figure 39). A sesamoid bone is a bone that is incorporated into the tendon of a muscle where that tendon crosses a joint. The sesamoid bone articulates with the underlying bones to prevent damage to the muscle tendon due to rubbing against the bones during movements of the joint. The patella is found in the tendon of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2875\">quadriceps femoris<\/a> muscle, the large muscle of the anterior thigh that passes across the anterior knee to attach to the tibia. The patella articulates with the patellar surface of the femur and thus prevents rubbing of the muscle tendon against the distal femur. The patella also lifts the tendon away from the knee joint, which increases the leverage power of the quadriceps femoris muscle as it acts across the knee. The patella does not articulate with the tibia.<\/p>\n<p style=\"text-align: justify\"><strong>Tibia:<\/strong> The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2748\">tibia<\/a> (shin bone) is the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2362\">medial<\/a> bone of the leg and is larger than the fibula, with which it is paired (Figure 40). The tibia is the main weight-bearing bone of the lower leg and the second longest bone of the body, after the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2379\">femur<\/a>. The medial side of the tibia is located immediately under the skin, allowing it to be easily palpated down the entire length of the medial leg.<\/p>\n<p style=\"text-align: justify\"><strong>Fibula:<\/strong> The fibula is the slender bone located on the lateral side of the leg (Figure 40). The fibula does not bear weight. It serves primarily for muscle attachments and thus is largely surrounded by muscles. Only the proximal and distal ends of the fibula can be palpated.<\/p>\n<p style=\"text-align: justify\"><strong>Tarsal Bones:<\/strong> The posterior half of the foot is formed by seven <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2753\">tarsal<\/a> bones (Figure 43). The most superior tarsal bone, the<strong> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2876\">talus<\/a><\/strong>, articulates with the tibia and fibula to form the <strong>ankle joint<\/strong>. Inferiorly, the talus articulates with the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2877\">calcaneus<\/a> <\/strong>(heel bone), the largest bone of the foot, which forms the heel. Body weight is transferred from the tibia to the talus to the calcaneus, which rests on the ground.<\/p>\n<figure style=\"width: 669px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image43-4.png\" alt=\"image\" width=\"669\" height=\"1046\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 39. Femur and Patella.<\/strong> The femur is the single bone of the thigh region. It articulates superiorly with the hip bone at the hip joint, and inferiorly with the tibia at the knee joint. The patella only articulates with the distal end of the femur.<\/figcaption><\/figure>\n<p style=\"text-align: justify\"><strong>Metatarsal Bones:<\/strong> The anterior half of the foot is formed by the five <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2743\">metatarsal<\/a> bones, which are located between the tarsal bones of the posterior foot and the phalanges of the toes (Figure 41). These elongated bones are numbered 1\u20135, starting with the medial side of the foot.<\/p>\n<p style=\"text-align: justify\"><strong>Phalanx bones:<\/strong> The toes contain a total of 14 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2750\">phalanx<\/a> bones (phalanges), arranged in a similar manner as the phalanges of the fingers (Figure 41). The toes are numbered 1\u20135, starting with the big toe (<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_1643_2404\">hallux<\/a><\/strong>). The big toe has two phalanx bones, the proximal and distal phalanges. The remaining toes all have proximal, middle, and distal phalanges. A joint between adjacent phalanx bones is called an interphalangeal joint.<\/p>\n<figure style=\"width: 844px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image44-2.png\" alt=\"image\" width=\"844\" height=\"1044\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 40. Tibia and Fibula.<\/strong> The tibia is the larger, weight-bearing bone located on the medial side of the leg. The fibula is the slender bone of the lateral side of the leg and does not bear weight.<\/figcaption><\/figure>\n<figure style=\"width: 1118px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-content\/uploads\/sites\/750\/2019\/08\/image45-2.png\" alt=\"image\" width=\"1118\" height=\"814\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 41. Bones of the Foot.<\/strong> The bones of the foot are divided into three groups. The posterior foot is formed by the seven tarsal bones. The mid-foot has the five metatarsal bones. The toes contain the phalanges.<\/figcaption><\/figure>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><a id=\"P\"><\/a>Practice Questions<\/p>\n<\/header>\n<div class=\"textbox__content\">\n<p><strong>A. Bone Tissue and the Skeletal System<\/strong><\/p>\n<p><strong>Part 1:<\/strong> The Functions of the Skeletal System<\/p>\n<div id=\"h5p-10\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-10\" class=\"h5p-iframe\" data-content-id=\"10\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-1 230\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part 2: Bone Classification<\/strong><\/p>\n<div id=\"h5p-15\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-15\" class=\"h5p-iframe\" data-content-id=\"15\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-2 235\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-16\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-16\" class=\"h5p-iframe\" data-content-id=\"16\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-3 236\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part 3: Bone Structure<\/strong><\/p>\n<div id=\"h5p-11\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-11\" class=\"h5p-iframe\" data-content-id=\"11\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-4 231\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-12\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-12\" class=\"h5p-iframe\" data-content-id=\"12\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-5 232\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-13\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-13\" class=\"h5p-iframe\" data-content-id=\"13\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-6 233\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-14\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-14\" class=\"h5p-iframe\" data-content-id=\"14\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-6 234\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-17\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-17\" class=\"h5p-iframe\" data-content-id=\"17\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-8 237\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-21\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-21\" class=\"h5p-iframe\" data-content-id=\"21\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-10 241\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-22\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-22\" class=\"h5p-iframe\" data-content-id=\"22\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-11 242\"><\/iframe><\/div>\n<\/div>\n<p><strong>Part 4: Bone Formation and Development<\/strong><\/p>\n<div id=\"h5p-18\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-18\" class=\"h5p-iframe\" data-content-id=\"18\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-12 238\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-19\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-19\" class=\"h5p-iframe\" data-content-id=\"19\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-13 239\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-40\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-40\" class=\"h5p-iframe\" data-content-id=\"40\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-14 259\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-23\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-23\" class=\"h5p-iframe\" data-content-id=\"23\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-15 243\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-25\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-25\" class=\"h5p-iframe\" data-content-id=\"25\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-16 244\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-39\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-39\" class=\"h5p-iframe\" data-content-id=\"39\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-21 258\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-26\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-26\" class=\"h5p-iframe\" data-content-id=\"26\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-17 245\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-28\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-28\" class=\"h5p-iframe\" data-content-id=\"28\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-18 246\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-30\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-30\" class=\"h5p-iframe\" data-content-id=\"30\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-20 247\"><\/iframe><\/div>\n<\/div>\n<p><strong style=\"text-align: initial;font-size: 1em\">Part 5: Fractures<\/strong><\/p>\n<div id=\"h5p-31\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-31\" class=\"h5p-iframe\" data-content-id=\"31\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-22 249\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-32\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-32\" class=\"h5p-iframe\" data-content-id=\"32\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-23 250\"><\/iframe><\/div>\n<\/div>\n<p><strong style=\"text-align: initial;font-size: 1em\">B. Skeletal Anatomy<\/strong><\/p>\n<p><strong style=\"text-align: initial;font-size: 1em\">Part 1: The <\/strong><strong style=\"text-align: initial;font-size: 1em\">Axial Skeleton<\/strong><\/p>\n<div id=\"h5p-33\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-33\" class=\"h5p-iframe\" data-content-id=\"33\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-24 251\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-34\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-34\" class=\"h5p-iframe\" data-content-id=\"34\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-25 252\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-35\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-35\" class=\"h5p-iframe\" data-content-id=\"35\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-26 253\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-37\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-37\" class=\"h5p-iframe\" data-content-id=\"37\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-28 254\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-36\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-36\" class=\"h5p-iframe\" data-content-id=\"36\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-27 255\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-41\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-41\" class=\"h5p-iframe\" data-content-id=\"41\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-30 256\"><\/iframe><\/div>\n<\/div>\n<p><strong style=\"text-align: initial;font-size: 1em\">Part 2. The Appendicular Skeleton<\/strong><\/p>\n<div id=\"h5p-43\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-43\" class=\"h5p-iframe\" data-content-id=\"43\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-32 260\"><\/iframe><\/div>\n<\/div>\n<div id=\"h5p-44\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-44\" class=\"h5p-iframe\" data-content-id=\"44\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"12-32 261\"><\/iframe><\/div>\n<\/div>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_1643_2737\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2737\"><div tabindex=\"-1\"><p>Tube composed of cartilaginous rings and supporting tissue that connects the lung bronchi and the larynx; provides a route for air to enter and exit the lung.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2738\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2738\"><div tabindex=\"-1\"><p>cartilaginous structure that produces the voice, prevents food and beverages from entering the trachea, and regulates the volume of air that enters and leaves the lungs<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2735\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2735\"><div tabindex=\"-1\"><p>Strong connective tissue bands that hold the bones at a moveable joint together.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2736\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2736\"><div tabindex=\"-1\"><p>Dense regular connective tissue that attaches skeletal muscle to bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2739\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2739\"><div tabindex=\"-1\"><p>Simple machine consisting of a beam or rigid rod (bone) pivoted at a fixed hinge, or fulcrum (joint).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2740\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2740\"><div tabindex=\"-1\"><p>Site at which two or more bones or bone and cartilage come together (articulate).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2298\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2298\"><div tabindex=\"-1\"><p>Fluid or semi-fluid portion of the matrix.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2742\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2742\"><div tabindex=\"-1\"><p>Connective tissue in the interior cavity of a bone where fat is stored.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2300\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2300\"><div tabindex=\"-1\"><p>Specialized areolar tissue rich in stored fat.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2741\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2741\"><div tabindex=\"-1\"><p>Connective tissue in the interior cavity of a bone where hematopoiesis takes place.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2329\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2329\"><div tabindex=\"-1\"><p>(Also, hematopoiesis) production of the formed elements of blood.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2328\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2328\"><div tabindex=\"-1\"><p>(Also, thrombocytes) one of the formed elements of blood that consists of cell fragments broken off from megakaryocytes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2746\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2746\"><div tabindex=\"-1\"><p>Single bone of the upper arm.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2745\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2745\"><div tabindex=\"-1\"><p>Bone located on the medial side of the forearm.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2747\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2747\"><div tabindex=\"-1\"><p>Bone located on the lateral side of the forearm.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2379\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2379\"><div tabindex=\"-1\"><p>Thigh bone; the single bone of the thigh.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2748\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2748\"><div tabindex=\"-1\"><p>Shin bone; the large, weight-bearing bone located on the medial side of the leg.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2749\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2749\"><div tabindex=\"-1\"><p>Thin, non-weight-bearing bone found on the lateral side of the leg.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2744\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2744\"><div tabindex=\"-1\"><p>One of the five long bones that form the palm of the hand; numbered 1\u20135, starting on the lateral (thumb) side of the hand.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2743\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2743\"><div tabindex=\"-1\"><p>One of the five elongated bones that forms the anterior half of the foot; numbered 1\u20135, starting on the medial side of the foot.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2750\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2750\"><div tabindex=\"-1\"><p>(plural = phalanges) one of the bones that form the fingers or toes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2752\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2752\"><div tabindex=\"-1\"><p>One of the eight small bones that form the wrist and base of the hand; these are grouped as a proximal row consisting of (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones, and a distal row containing (from lateral to medial) the trapezium, trapezoid, capitate, and hamate bones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2753\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2753\"><div tabindex=\"-1\"><p>One of the seven bones that make up the posterior foot; includes the calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform bones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2755\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2755\"><div tabindex=\"-1\"><p>Shoulder blade bone located on the posterior side of the shoulder.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2754\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2754\"><div tabindex=\"-1\"><p>Flattened bone located at the center of the anterior chest.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2408\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2408\"><div tabindex=\"-1\"><p>Knee cap.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2756\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2756\"><div tabindex=\"-1\"><p>Tubular shaft that runs between the proximal and distal ends of a long bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2757\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2757\"><div tabindex=\"-1\"><p>Wide section at each end of a long bone; filled with spongy bone and red marrow.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2758\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2758\"><div tabindex=\"-1\"><p>Hollow region of the diaphysis; filled with yellow marrow.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2759\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2759\"><div tabindex=\"-1\"><p>Dense osseous tissue that can withstand compressive forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2327\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2327\"><div tabindex=\"-1\"><p>(Also, cancellous bone) trabeculated osseous tissue that supports shifts in weight distribution.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2760\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2760\"><div tabindex=\"-1\"><p>(Also, growth plate) sheet of hyaline cartilage in the metaphysis of an immature bone; replaced by bone tissue as the organ grows in length.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2321\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2321\"><div tabindex=\"-1\"><p>Most common type of cartilage, smooth and made of short collagen fibers embedded in a chondroitin sulfate ground substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2761\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2761\"><div tabindex=\"-1\"><p>completely ossified remnant of the epiphyseal plate<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2762\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2762\"><div tabindex=\"-1\"><p>Delicate membranous lining of a bone\u2019s medullary cavity.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2764\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2764\"><div tabindex=\"-1\"><p>Fibrous membrane covering the outer surface of bone and continuous with ligaments.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2763\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2763\"><div tabindex=\"-1\"><p>Thin layer of cartilage covering an epiphysis; reduces friction and acts as a shock absorber.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2765\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2765\"><div tabindex=\"-1\"><p>Layer of spongy bone, that is sandwiched between two the layers of compact bone found in flat bones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2174\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2174\"><div tabindex=\"-1\"><p>The most abundant of three protein fibres found in the extracellular matrix of connective tissues.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2324\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2324\"><div tabindex=\"-1\"><p>A form of calcium phosphate mineral found in bones (also hydroxylapatite)<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2766\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2766\"><div tabindex=\"-1\"><p>Cell responsible for forming new bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2325\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2325\"><div tabindex=\"-1\"><p>Primary cell in mature bone; responsible for maintaining the matrix.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2318\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2318\"><div tabindex=\"-1\"><p>(Plural= lacunae) small spaces in bone or cartilage tissue that cells occupy.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2767\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2767\"><div tabindex=\"-1\"><p>(Singular = canaliculus) channels within the bone matrix that house one of an osteocyte\u2019s many cytoplasmic extensions that it uses to communicate and receive nutrients.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2709\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2709\"><div tabindex=\"-1\"><p>Division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed. Usually immediately followed by cytokinesis (cell division).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2770\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2770\"><div tabindex=\"-1\"><p>Undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2768\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2768\"><div tabindex=\"-1\"><p>Cell responsible for resorbing bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2769\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2769\"><div tabindex=\"-1\"><p>Precursor to macrophages and dendritic cells seen in the blood.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2307\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2307\"><div tabindex=\"-1\"><p>Ameboid (irregular outline with peripheral projections) phagocyte found in several tissues throughout the body.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2771\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2771\"><div tabindex=\"-1\"><p>(Also, Haversian system) basic structural unit of compact bone; made of concentric layers of calcified matrix.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2774\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2774\"><div tabindex=\"-1\"><p>Concentric rings of calcified matrix that form an osteon.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2772\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2772\"><div tabindex=\"-1\"><p>(Also Haversian canal) longitudinal channel in the center of each osteon; contains blood vessels, nerves, and lymphatic vessels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2773\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2773\"><div tabindex=\"-1\"><p>(Also, Volkmann\u2019s canal) channel that branches off from the central canal and houses vessels and nerves that extend to the periosteum and endosteum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2775\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2775\"><div tabindex=\"-1\"><p>(Singular= trabecula) spikes or sections of the lattice-like matrix in spongy bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2783\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2783\"><div tabindex=\"-1\"><p>Small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2784\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2784\"><div tabindex=\"-1\"><p>(Also, osteogenesis) bone formation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2785\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2785\"><div tabindex=\"-1\"><p>Process by which bone forms directly from mesenchymal tissue.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2792\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2792\"><div tabindex=\"-1\"><p>Process in which bone forms by replacing hyaline cartilage.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2788\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2788\"><div tabindex=\"-1\"><p>Cell responsible for forming new cartilage.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2286\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2286\"><div tabindex=\"-1\"><p>Lacking blood vessels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2306\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2306\"><div tabindex=\"-1\"><p>Embryonic tissue from which connective tissue cells derive.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2786\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2786\"><div tabindex=\"-1\"><p>Collarbone; elongated bone that articulates with the manubrium of the sternum medially and the acromion of the scapula laterally.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2789\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2789\"><div tabindex=\"-1\"><p>Cluster of osteoblasts found in the early stages of intramembranous ossification.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2790\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2790\"><div tabindex=\"-1\"><p>Uncalcified bone matrix secreted by osteoblasts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2791\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2791\"><div tabindex=\"-1\"><p>Region, deep in the periosteal collar, where bone development starts during endochondral ossification.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2977\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2977\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2319\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2319\"><div tabindex=\"-1\"><p>Layer of dense irregular connective tissue surrounding cartilage.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2320\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2320\"><div tabindex=\"-1\"><p>cartilage cells<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2793\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2793\"><div tabindex=\"-1\"><p>Region of bone development in the epiphyses.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2807\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2807\"><div tabindex=\"-1\"><p>Region of the epiphyseal plate that anchors the plate to the osseous tissue of the epiphysis.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2808\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2808\"><div tabindex=\"-1\"><p>Region of the epiphyseal plate that makes new chondrocytes to replace those that die at the diaphyseal end of the plate and contributes to longitudinal growth of the epiphyseal plate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2809\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2809\"><div tabindex=\"-1\"><p>Region of the epiphyseal plate where chondrocytes from the proliferative zone grow and mature and contribute to the longitudinal growth of the epiphyseal plate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2810\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2810\"><div tabindex=\"-1\"><p>Region of the epiphyseal plate closest to the diaphyseal end; functions to connect the epiphyseal plate to the diaphysis.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2297\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2297\"><div tabindex=\"-1\"><p>(In connective tissue) extracellular material which is produced by the cells embedded in it, containing ground substance and fibres.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2812\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2812\"><div tabindex=\"-1\"><p>Central, vertical axis of the body, including the skull, vertebral column, and thoracic cage.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2815\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2815\"><div tabindex=\"-1\"><p>Entire sequence of bones that extend from the skull to the tailbone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2816\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2816\"><div tabindex=\"-1\"><p>Consists of 12 pairs of ribs and sternum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2813\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2813\"><div tabindex=\"-1\"><p>Small, U-shaped bone located in upper neck that does not contact any other bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2611\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2611\"><div tabindex=\"-1\"><p>Three small bones in the middle ear.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2818\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2818\"><div tabindex=\"-1\"><p>Individual bone in the neck and back regions of the vertebral column.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2817\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2817\"><div tabindex=\"-1\"><p>Single bone located near the inferior end of the adult vertebral column that is formed by the fusion of five sacral vertebrae; forms the posterior portion of the pelvis.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2409\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2409\"><div tabindex=\"-1\"><p>Lowest part of the vertebral column; 'tailbone'<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2357\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2357\"><div tabindex=\"-1\"><p>Describes the front or direction toward the front of the body; also referred to as ventral.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2819\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2819\"><div tabindex=\"-1\"><p>Fourteen bones that support the facial structures and form the upper and lower jaws and the hard palate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2820\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2820\"><div tabindex=\"-1\"><p>Unpaired bone that forms the lower jaw bone; the only moveable bone of the skull.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2821\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2821\"><div tabindex=\"-1\"><p>Expanded area of fibrous connective tissue that separates the brain case bones of the skull prior to birth and during the first year after birth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2822\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2822\"><div tabindex=\"-1\"><p>Fibrous joint that connects the bones of the skull (except the mandible); an immobile joint (synarthrosis).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2391\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2391\"><div tabindex=\"-1\"><p>Division of the posterior (dorsal) cavity that houses the brain.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2823\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2823\"><div tabindex=\"-1\"><p>Paired bones that form the upper, lateral sides of the skull.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2824\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2824\"><div tabindex=\"-1\"><p>Paired bones that form the lateral, inferior portions of the skull, with squamous, mastoid, and petrous portions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2825\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2825\"><div tabindex=\"-1\"><p>Unpaired bone that forms forehead, roof of orbit, and floor of anterior cranial fossa.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2826\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2826\"><div tabindex=\"-1\"><p>Unpaired bone that forms the posterior portions of the brain case and base of the skull.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2827\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2827\"><div tabindex=\"-1\"><p>Unpaired bone that forms the central base of skull.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2828\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2828\"><div tabindex=\"-1\"><p>Unpaired bone that forms the roof and upper, lateral walls of the nasal cavity, portions of the floor of the anterior cranial fossa and medial wall of orbit, and the upper portion of the nasal septum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2620\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2620\"><div tabindex=\"-1\"><p>Paired bones that form the lateral, inferior portions of the skull, with squamous, mastoid, and petrous portions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2832\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2832\"><div tabindex=\"-1\"><p>(Also, maxilla) paired bones that form the upper jaw and anterior portion of the hard palate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2843\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2843\"><div tabindex=\"-1\"><p>anterior portion of each vertebra that supports the body weight.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2840\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2840\"><div tabindex=\"-1\"><p>Bony arch formed by the posterior portion of each vertebra that surrounds and protects the spinal cord.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2842\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2842\"><div tabindex=\"-1\"><p>Opening associated with each vertebra defined by the vertebral arch that provides passage for the spinal cord.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2841\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2841\"><div tabindex=\"-1\"><p>Bony passageway within the vertebral column for the spinal cord that is formed by the series of individual vertebral foramina.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2858\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2858\"><div tabindex=\"-1\"><p>Paired bony processes that extends laterally from the vertebral arch of a vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2844\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2844\"><div tabindex=\"-1\"><p>Unpaired bony process that extends posteriorly from the vertebral arch of a vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2845\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2845\"><div tabindex=\"-1\"><p>Bony process that extends upward from the vertebral arch of a vertebra that articulates with the inferior articular process of the next higher vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2846\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2846\"><div tabindex=\"-1\"><p>Bony process that extends downward from the vertebral arch of a vertebra that articulates with the superior articular process of the next lower vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2847\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2847\"><div tabindex=\"-1\"><p>Paired bony processes that extends laterally from the vertebral arch of a vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2848\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2848\"><div tabindex=\"-1\"><p>First cervical (C1) vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2849\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2849\"><div tabindex=\"-1\"><p>Second cervical (C2) vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2850\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2850\"><div tabindex=\"-1\"><p>Bony projection (odontoid process) that extends upward from the body of the C2 (axis) vertebra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2851\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2851\"><div tabindex=\"-1\"><p>Expanded, superior portion of the sternum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2852\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2852\"><div tabindex=\"-1\"><p>Small process that forms the inferior tip of the sternum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2853\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2853\"><div tabindex=\"-1\"><p>Hyaline cartilage structure attached to the anterior end of each rib that provides for either direct or indirect attachment of most ribs to the sternum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2854\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2854\"><div tabindex=\"-1\"><p>Vertebrosternal ribs 1\u20137 that attach via their costal cartilage directly to the sternum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2855\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2855\"><div tabindex=\"-1\"><p>Vertebrochondral ribs 8\u201312 whose costal cartilage either attaches indirectly to the sternum via the costal cartilage of the next higher rib or does not attach to the sternum at all.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2856\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2856\"><div tabindex=\"-1\"><p>Vertebral ribs 11\u201312 that do not attach to the sternum or to the costal cartilage of another rib.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2860\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2860\"><div tabindex=\"-1\"><p>All bones of the upper and lower limbs, plus the girdle bones that attach each limb to the axial skeleton.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2859\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2859\"><div tabindex=\"-1\"><p>An encircling or confining structure; in anatomy, the pectoral or pelvic girdle.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2861\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2861\"><div tabindex=\"-1\"><p>Shoulder girdle; the set of bones, consisting of the scapula and clavicle, which attaches each upper limb to the axial skeleton.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2862\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2862\"><div tabindex=\"-1\"><p>Hip girdle; consists of a single hip bone, which attaches a lower limb to the sacrum of the axial skeleton.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2362\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2362\"><div tabindex=\"-1\"><p>Describes the middle or direction toward the middle of the body.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2358\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2358\"><div tabindex=\"-1\"><p>Describes the back or direction toward the back of the body; also referred to as dorsal.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2361\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2361\"><div tabindex=\"-1\"><p>Describes the side or direction toward the side of the body.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2863\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2863\"><div tabindex=\"-1\"><p>(Also, glenoid fossa) shallow depression located on the lateral scapula, between the superior and lateral borders.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2864\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2864\"><div tabindex=\"-1\"><p>Shoulder joint; formed by the articulation between the glenoid cavity of the scapula and the head of the humerus.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2373\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2373\"><div tabindex=\"-1\"><p>Describes a position in a limb that is nearer to the point of attachment or the trunk of the body.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2865\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2865\"><div tabindex=\"-1\"><p>Wrist joint, located between the forearm and hand regions of the upper limb; articulation formed proximally by the distal end of the radius and the fibrocartilaginous pad that unites the distal radius and ulna bone, and distally by the scaphoid, lunate, and triquetrum carpal bones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2374\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2374\"><div tabindex=\"-1\"><p>Describes a position in a limb that is farther from the point of attachment or the trunk of the body.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2405\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2405\"><div tabindex=\"-1\"><p>Thumb<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2866\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2866\"><div tabindex=\"-1\"><p>Articulation between adjacent phalanx bones of the hand or foot digits.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2867\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2867\"><div tabindex=\"-1\"><p>Superior portion of the hip bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2868\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2868\"><div tabindex=\"-1\"><p>Superior portion of the hip bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2869\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2869\"><div tabindex=\"-1\"><p>Anterior portion of the hip bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2870\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2870\"><div tabindex=\"-1\"><p>Joint formed by the articulation between the auricular surfaces of the sacrum and ilium.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2871\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2871\"><div tabindex=\"-1\"><p>Joint formed by the articulation between the pubic bodies of the right and left hip bones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2872\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2872\"><div tabindex=\"-1\"><p>Large, roughened protuberance that forms the posteroinferior portion of the hip bone; weight-bearing region of the pelvis when sitting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2873\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2873\"><div tabindex=\"-1\"><p>Large, U-shaped indentation located on the posterior margin of the ilium, superior to the ischial spine.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2874\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2874\"><div tabindex=\"-1\"><p>A bone embedded in tendon; the only major sesamoid bone is the patella.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2875\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2875\"><div tabindex=\"-1\"><p>Muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2876\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2876\"><div tabindex=\"-1\"><p>Tarsal bone that articulates superiorly with the tibia and fibula at the ankle joint; also articulates inferiorly with the calcaneus bone and anteriorly with the navicular bone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2877\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2877\"><div tabindex=\"-1\"><p>Heel bone; posterior, inferior tarsal bone that forms the heel of the foot.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_1643_2404\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_1643_2404\"><div tabindex=\"-1\"><p>Big toe<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":10,"menu_order":2,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1643","chapter","type-chapter","status-publish","hentry"],"part":337,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1643","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/users\/10"}],"version-history":[{"count":25,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1643\/revisions"}],"predecessor-version":[{"id":3256,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1643\/revisions\/3256"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/parts\/337"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapters\/1643\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/media?parent=1643"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/pressbooks\/v2\/chapter-type?post=1643"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/contributor?post=1643"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/dcbiol110311092nded\/wp-json\/wp\/v2\/license?post=1643"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}