A fleshy muscle covering the posterior half of the external surface of the scapula.

Origin. - From the entire outer surface of the bone behind the central ridge or scapular spine.

Insertion. - By two short tendons, one into the outer tubercle of the humerus, the other into the upper part of the ridge beneath it. A synovial bursa intervenes between the latter and the external tubercle over which it plays.

Action. - It abducts the humerus or upper arm and rotates it outwards.