Teres minor is completely hidden beneath the deltoid. It arises from an elongated oval area at the axillary border of the scapula. It passes upwards and laterally, edge to edge with the lower border of infraspinatus, to the lowest facet on the greater tuberosity of the humerus and to a thumb’s breadth of bone below this. It passes behind the origin of the long head of triceps. At the lower border it lies edge to edge with teres major at its origin, but the latter muscle leaves it by passing forward in front of the long head of triceps. Triceps long head thus makes a triangular space between these muscles on the scapular side and a quadrilateral space on the humeral side.
Nerve supply of teres minor:
By a branch from the posterior branch of the axillary nerve (C5 and 6), from the posterior cord of the brachial plexus.
Action of teres minor:
It assists the other small muscles around the head of the humerus in steadying the shoulder joint in movements of peripheral parts of the limb. More specifically, it can act as a lateral rotator and weak adductor of the humerus. With the teres major it holds down the head of the humerus against the upward pull of the deltoid during abduction of the shoulder.