Evolution of the Shoulder Girdle with Special Reference to the Problems of the Clavicle

Persistent problems involving the clavicle include the reason for its reduction in many mammals, its function in hominids, the last ossification, and so on. In this paper these problems are considered from the point of views of comparative and functional morphology. The clavicle is an element of the dermal shoulder girdle that is in the process of reduction through tetrapod evolution. The reason why the clavicle disappeared or was reduced in cursorial mammals is probably that it disturbed the reciprocal movement of the scapula. The human clavicle works also as a supporter of the forelimb. The characteristic double-curved form of the clavicle may be related to its function. The sternal epiphysis of the clavicle fuses last among the long bones of the human skeleton, in spite of the first ossification of the clavicular body. The delay of determination of the clavicular length should be convenient to slight adjustment for retaining dynamic stability in human bipedal walking.