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Upper limb - bones of
Other Terms: Superior limb, Upper limb
The proximal end of the superior appendage, the clavicle and scapula, is the pectoral or shoulder girdle. This girdle of bones provides a broad base of support and through muscles, rather than ligaments, helps anchor the limb to the axial skeleton. The humerus forms the skeletal framework for the next region of the appendage, the brachium. Distal to the brachium is the antebrachium containing the radius and ulna. The distal most region of the superior limb is the hand consisting of a eight carpal bones, five metacarpal bones, and fourteen phalanges.
Superior is from the Latin word supra meaning above. Appendage is Latin meaning to hang to or from. It comes from the Latin ad meaning to and pendere, the verb to hang. Limb arises from the Anglo-Saxon word lim. This word means a branch and has come to mean an arm or leg because they branch from the trunk.
The shoulder girdle forms a joint with the brachial element, the humerus, at the highly mobile ball-and-socket joint of the shoulder. Distally the humerus joins the radius and ulna to form the hinge-like elbow joint. The radius and the ulna form a pivot joint between them called the radio-ulnar joint allowing for supination and pronation of the hand. Distally the radius articulates with the carpal bones forming a bi-axial ellipsoid joint. The hand exhibits a variety of joints, from the plane joints between the carpal bones to the hinge joints between the phalanges.
All the bones of the limbs ossify endochonrally. During this endochondral ossification the long bones of the limbs develop synchondrotic joints called epiphyseal growth plates. These cartilage plates form the growth centers during the early years (up to age 25) of postnatal life. Some general rules for ossification patterns in these bones are: 1) primary ossification centers appear during the end of the embryonic period; 2) secondary ossification centers appear near the time of birth; 3) secondary centers typically appear earlier in females; 4) secondary centers that appear early will usually fuse later.