The clavicle (collar bone) extends from the manubrium of the sternum, to the scapula. It helps make up the shoulder girdle (pectoral girdle). The word clavicle is derived from the Latin word 'clavicula', Latin for little key. The 'little key' reference, pertains to the fact that the clavicle rotates along its axis, similar to the movement of a key in a keyhole, when the shoulder is abducted. In some people, particularly females whom may have less fat in this region, the location of the bone is clearly visible, as it protrudes through the skin. The clavicle bone is easily identifiable in people with underdeveloped pectoralis muscles.