scapula

Large, flat, triangular bone which lies over the second to seventh ribs on the back, forming part of the pectoral girdle, and assisting in the articulation of the arm with the chest region. Its flattened shape allows a large region for the attachment of muscles.

The costal or deep surface of the scapula is smooth and concave, whilst an almost horizontal spine divides the dorsal surface in two. This spine continues laterally as a shelf of bone, the acromion, which forms the tip of the shoulder in humans. The scapula is joined to the clavicle (collarbone) at the acromion, and the humerus (arm bone) fits into the glenoid cavity just below. The coracoid process is an anterior projection of the superior edge of the scapula. The scapula is well protected by thick muscular coverings and is rarely fractured.