SKELETAL SYSTEM OUTLINE 8.1 Pectoral Girdle 221 8.1a Clavicle 221 8 8.1b Scapula 221 8.2 Upper Limb 225 8.2a Humerus 225 8.2b Radius and Ulna 225 8.2c Carpals, Metacarpals, and Phalanges 230 Appendicular 8.3 Pelvic Girdle 232 8.3a Os Coxae 232 8.3b True and False Pelves 233 8.3c Sex Differences Between the Female and Male Skeleton Pelves 233 8.4 Lower Limb 236 8.4a Femur 237 8.4b Patella 240 8.4c Tibia and Fibula 240 8.4d Tarsals, Metatarsals, and Phalanges 241 8.5 Aging of the Appendicular Skeleton 245 8.6 Development of the Appendicular Skeleton 245 MODULE 5: SKELETAL SYSTEM mck78097_ch08_220-251.indd 220 2/14/11 2:51 PM Chapter Eight Appendicular Skeleton 221 ne benefit of space travel is that it has helped advance our mion of the scapula (figure 8.2). It is the only direct connection O knowledge of human anatomy. We are excited and amazed between the pectoral girdle and the axial skeleton. Its sternal by video showing astronauts in space running on treadmills, riding end (medial end) is roughly pyramidal in shape and articulates stationary bicycles, jumping rope, and doing various other exercises. with the manubrium of the sternum, forming the sternoclavicular For astronauts—as for all of us—exercise is essential for maintain- joint. The acromial end (lateral end) of the clavicle is broad and ing bone mass and strength as well as muscle tone and strength. flattened. The acromial end articulates with the acromion of the When we exercise on Earth, our contracting muscles work with scapula, forming the acromioclavicular joint. and against gravity applying stress to the bones to which they are You can palpate your own clavicle by first locating the supe- attached, thereby strengthening the bone and ultimately preventing rior aspect of your sternum and then moving your hand laterally. it from becoming thin and brittle. Regular exercise prevents degen- The curved bone you feel under your skin, and close to the collar erative changes in the skeleton and helps us avoid serious health of your shirt, is your clavicle. problems later in life. The superior surface of the clavicle is relatively smooth, but When we exercise, we move the bones of the appendicular the inferior surface is marked by grooves and ridges for muscle and skeleton, which includes the bones of the upper and lower limbs, ligament attachments. On the inferior surface, near the acromial and the girdles of bones that hold and attach the upper and lower end, is a rough tuberosity called the conoid (kō ̄ ́noyd; konoeides = limbs to the axial skeleton (figure 8.1). The pectoral girdle con- cone-shaped) tubercle. The inferiorly located prominence at the sists of bones that hold the upper limbs in place, while the pelvic sternal end of the clavicle is called the costal tuberosity. girdle consists of bones that hold the lower limbs in place. In this chapter, we examine the specific components of the appendicular 8.1b Scapula skeleton and explore their interactions with other systems, such The scapula (skap ́ū -lă ) is a broad, flat, triangular bone that as the muscular and cardiovascular systems. Be sure to review forms the “shoulder blade” (figure 8.3). You can palpate your figure 6.17 regarding bone feature names before you proceed. scapula by putting your hand on your superolateral back region and moving your upper limb; the bone you feel moving is the scapula. Several large projections extend from the scapula and Study Tip! provide surface area for muscle and ligament attachments. The spine of the scapula is a ridge of bone on the posterior aspect Many bones and bony features may be palpated (felt) underneath of the scapula. It is easily palpated under the skin. The spine is the skin. As you hold a bone in lab, try to palpate the same bone on your continuous with a larger, posterior process called the acromion own body. In this way, you will understand how the bone is positioned, (ă-krō ḿ ē -on; akron = tip, omos = shoulder), which forms the how it associates with other bones, and how it moves in a living body. bony tip of the shoulder. Palpate the superior region of your In effect, you can use your body as a “bone study guide.” shoulder; the prominent bump you feel is the acromion. The acromion articulates with the acromial end of the clavicle. The coracoid (kō r ́ă-koyd; korakodes = like a crow’s beak) process is the smaller, more anterior projection. The triangular shape of the scapula forms three sides, or 8.1 Pectoral Girdle borders. The superior border is the horizontal edge of the scapula Learning Objectives: superior to the spine of the scapula; the medial border (also called the vertebral border) is the edge of the scapula closest to the 1. Name the bones of the pectoral girdle and describe their functions. 2. Identify the bone surface features in the pectoral girdle. The left and right pectoral (pek t́ ŏ -ră l; pectus = breastbone) girdles (ger ́dl) articulate with the trunk, and each supports CLINICAL VIEW one upper limb. A pectoral girdle consists of two bones: the clavicle (collarbone) and the scapula (shoulder blade). The pec- Fracture of the Clavicle toral girdle also provides attachment sites for many muscles that move the limb, and it promotes upper limb mobility in two ways: The clavicle can fracture relatively easily because its S shape does (1) Because the scapula is not directly attached to the axial skel- not allow it to resist stress. In addition, the sternoclavicular joint eton, it moves freely across the posterior surface of the thorax, is incredibly strong, so if stress is placed on both the clavicle and permitting the arm to move with it; and (2) the shallow cavity the joint, the clavicle will fracture before the joint is damaged. of the shoulder joint permits a wide range of movement of the A direct blow to the middle part of the clavicle, a fall onto the upper limb. lateral border of the shoulder, or use of the arms to brace against a forward fall is often stress enough to fracture the clavicle. WHAT DO YOU THINK? Because the clavicle has an anterior and posterior curve along its length between the medial and lateral edges, severe stress to the ●1 Why is the clavicle commonly known as the “collarbone”? Based on mid-region of the bone usually results in an anterior fracture. A this layman’s term, can you figure out where the clavicle is located in your body? posterior fracture may be more serious because bone splinters can penetrate the subclavian artery and vein, which lie immediately 8.1a Clavicle posterior and inferior to the clavicle and are the primary blood vessels supplying the upper limb. The clavicle (klav ́i-kl; clavis = key) is an S-shaped bone that extends between the manubrium of the sternum and the acro- mck78097_ch08_220-251.indd 221 2/14/11 2:51 PM 222 Chapter Eight Appendicular Skeleton Pectoral girdle Clavicle Scapula Upper limb Humerus Ulna Radius Carpals Metacarpals Phalanges Pelvic girdle Os coxae Lower limb Femur Patella Fibula Tibia Tarsals Metatarsals Phalanges (a) Anterior view (b) Posterior view Bones of the Appendicular Skeleton (63 bones per each side of the body, 126 bones total) Pectoral girdles Clavicle (2) Pelvic girdles Os coxae (2) (2 bones per (1 bone per each llium, ischium, and pubis bones fuse each girdle, Scapula (2) girdle, 2 bones total) in early adolescence 4 bones total) Lower limbs Femur (2) Upper limbs Humerus (2) (30 bones per (30 bones per each lower limb, Patella (2) each upper limb, Radius (2) 60 bones total) 60 bones total) Tibia (2) Ulna (2) Fibula (2) Carpals (16) Scaphoid (2), lunate (2), triquetrum (2), pisiform (2), Tarsals (14) trapezium (2), trapezoid (2), capitate (2), hamate (2) Calcaneus (2), talus (2), navicular (2), cuboid (2), medial cuneiform (2), intermediate cuneiform (2), Metacarpals (10) lateral cuneiform (2) Phalanges (28) Metatarsals (10) Proximal phalanx (10), middle phalanx (8), distal phalanx (10) Phalanges (28) Proximal phalanx (10), middle phalanx (8), distal phalanx (10) Figure 8.1 Appendicular Skeleton. (a) Anterior and (b) posterior views show the pectoral and pelvic girdles and the bones of the upper and lower limbs, all of which make up the appendicular skeleton. A table summarizes the bones of each region. mck78097_ch08_220-251.indd 222 2/14/11 2:51 PM Chapter Eight Appendicular Skeleton 223 Posterior Lateral Medial Anterior Sternal end Acromial end (a) Superior view, right clavicle Conoid tubercle Acromial end Anterior Sternal end Costal Lateral Medial tuberosity (b) Inferior view, right clavicle Posterior Acromial Coracoid Glenoid Sternal Head of Glenoid Coracoid Acromion end process cavity end humerus Acromion cavity process Clavicle Subscapular fossa Clavicle Subscapular fossa (c) Right scapula and clavicle articulation, anterior view (d) Radiograph of right shoulder Figure 8.2 Clavicle. The S-shaped clavicle is the only direct connection between the pectoral girdle and the axial skeleton. (a) Superior and (b) inferior views of the right clavicle. (c) Anterior view of an articulated right clavicle and scapula. (d) A radiograph of an articulated right clavicle and scapula. vertebrae; and the lateral border (also called the axillary border) is angle is composed primarily of the cup-shaped, shallow glenoid closest to the axilla (armpit). A conspicuous suprascapular notch (glē n oyd;́ resembling a socket) cavity, or glenoid fossa, which (which in some individuals is a suprascapular foramen) in the articulates with the humerus, the bone of the arm. Tubercles superior border provides passage for the suprascapular nerve.