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I. The Appendicular Skeleton
A. The appendicular skeleton consists of the pectoral and pelvic girdles and the bones of the upper and lower limbs.
II. The Pectoral Girdle
A. The pectoral girdle (shoulder girdle) is composed of a clavicle and scapula; the paired girdles do not form a complete ring as the term girdle implies.
1. Pectoral girdles are specialized for mobility and attach the upper limbs to the bony thorax.
B. The “S”-shaped clavicle (collarbone) functions as a brace for the shoulder; it also provides sites for muscle attachments.
1. Clavicles articulate with the sternum of the axial skeleton as well as the scapulae. Additionally, a ligament runs from the clavicle to the first rib.
C. The scapula articulates with a clavicle and humerus.
III. The Upper Limb
A. The upper limb (extremity) is made up of 30 bones and forms the arm, forearm, and hand; it is specialized for mobility.
B. The humerus is the only bone of the arm or brachium.
C. Two parallel long bones, the radius and ulna, form the skeleton of the forearm or antebrachium.
D. The skeleton of the hand includes the eight carpals of the wrist or carpus; the palm or metacarpus consists of five small long bones numbered 1–5; the digits or fingers consist of 14 miniature long bones called phalanges.
IV. The Pelvic Girdle
A. The pelvic girdle (hip girdle) attaches the lower limbs to the spine of the axial skeleton and supports visceral organs of the pelvis.
B. It is formed by a pair of coxal bones each consisting of three separate bones, the ilium, ischium, and pubis, that are fused in adults.
C. The coxal bones articulate with the sacrum to form the basin-like bony pelvis.
D. The female pelvis is modified in several ways to accommodate childbearing.
V. The Lower Limb
A. The three segments of the lower limb (extremity) are the thigh, leg, and foot; collectively, 30 bones compose the lower limb, and it is specialized for weight bearing and locomotion.
B. The femur is the only bone of the thigh.
C. The leg is the region between the knee and foot and it has two bones, the tibia and fibula.
D. The skeleton of the foot includes the seven tarsal bones of the tarsus; the metatarsus contains the five metatarsals numbered 1–5, and the digits or toes contain 14 phalanges.
E. The foot is supported by three arches that distribute the weight of the body to the heel and ball of the foot.
VI. Disorders of the Appendicular Skeleton
A. Most disorders are bone fractures; other significant disorders are birth defects, such as hip dysplasia and clubfoot.
VII. The Appendicular Skeleton Throughout Life
A. During growth, the arms and legs grow faster than the head and trunk
1. At birth, the head and trunk are roughly 1.5 times the length of the lower limbs
2. Lower limbs grow more rapidly than the trunk and age 10, the head and trunk are about the same length as the lower limbs.
B. After middle age, all bones lose bone mass; osteoporosis and limb fractures become more common.
|The Appendicular Skeleton|