The Appendicular Skeleton

The clavicle is a long bone, but it has no medullary cavity. The clavicle supports the scapula and arms, it protects deeper structures (blood vessels, for example) in the upper chest, and it transmits impact from the arms to the axial skeleton. The scapula is attached to the thorax and vertebral column by muscles. The pectoral girdles attach the upper extremities (limbs) to the axial skeleton and provide attachment sites for many muscles that move the upper limbs. The 2 pectoral girdles and the associated muscles form your shoulders.
The pectoral girdles are very flexible and allow the upper limbs a great deal of flexibility. They permit movement in many directions at the shoulder joint. The socket of the shoulder joint is small, shallow, and poorly reinforced with ligaments. This arrangement is good for flexibility, but it is not very stable. Shoulder dislocations are therefore fairly common. The UPPER LIMBS (extremities) (FIGS. 8. 4-8. 8) consist of 60 bones; 30 bones per limb. These are the bones of the arms, wrists, and hands.
They include the HUMERUS, ULNA, RADIUS, CARPALS, METACARPALS, and PHALANGES. The PELVIC GIRDLE (hip girdle) (FIGS. 8. 9-8. 11 & TABLE 8. 1) attaches the lower extremities (limbs) to the axial skeleton, and it supports and protects the visceral organs of the pelvic cavity. The pelvic girdle is a strong and stable support for the lower limbs. While the shoulder girdle moves somewhat freely and allows the arms a great deal of mobility, the pelvic girdle is secured to the axial skeleton by some of the strongest ligaments of the body.

Its sockets, which articulate with the thigh bones, are deep and cup-like and are heavily reinforced with ligaments. Even though both the shoulder and hip joints are ball-and-socket joints, the thigh cannot move in its socket with the same degree of freedom as the arm can in the shoulder joint. Flexibility in the hip joint is sacrificed for stability. The pelvic girdle consists of the 2 HIPBONES (coxal bones). Each hipbone of a newborn baby consists of 3 bones: the superior ILIUM, the inferior and anterior PUBIS, and the inferior and posterior ISCHIUM. Eventually these fuse into one COMPOSITE bone.
The area where they all fuse is called the ACETABULUM, which serves as the socket for the femur. The PUBIS of the hipbones meet anteriorly at the PUBIC SYMPHYSIS. The hipbones articulate posteriorly with the sacrum at the SACROILIAC JOINT. The 2 hipbones, with the sacrum and coccyx, form the basin-like structure called the PELVIS. The LOWER LIMBS (extremities) consists of 60 bones (FIG. 8. 12-8. 17); 30 bones per limb. These include the FEMUR (thighbone), PATELLA (kneecap), FIBULA & TIBIA (lower leg), TARSALS (anklebones and heel bones), METATARSALS (feet), and PHALANGES (toes).

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