_Insertion_ (Fig. 83, _c_).--By a flat tendon which passes over the capsule of the joint, into the ventral half of the infraspinatus fossa on the great tuberosity of the humerus. (The dorsal half of the fossa is covered by a synovial bursa.)
_Relations._--Outer surface with the spinotrapezius (Fig. 68, _j_), spinodeltoid (Fig. 68, _i_), acromiodeltoid (Fig. 68, _g_), teres major (Fig. 75, _d_), and levator scapulæ ventralis (Fig. 68, _f_). Inner surface with the scapula. Glenoid border with the teres minor (Fig. 80, _c_), the teres major (Fig. 75, _d_), and the long head of the triceps (Fig. 75, _g_).
=M. teres minor= (Fig. 80, _c_).--A small muscle from the glenoid border of the scapula to the proximal end of the humerus.
_Origin_ (Fig. 76, _e_) by a sheet of tendinous fibres from the glenoid border of the scapula beginning about one-fifth the length of the border from the glenoid fossa and extending to its middle. It is often attached to the infraspinatus (Fig. 80, _b_) and the caput longum of the triceps (Fig. 75, _g_).
_Insertion_ (Fig. 83, _d_) by a short tendon into the tubercle just distad of the infraspinatus fossa on the great tuberosity of the humerus.
_Relations._--Outer surface with the spinodeltoideus (Fig. 75, _e_), acromiodeltoideus (Fig. 75, _f_), and the infraspinatus (Fig. 80, _b_). Inner surface with the lateral (Fig. 75, _h_) and long (Fig. 75, _g_) heads of the triceps and the capsule of the joint.
_Action._--Assists the infraspinatus to rotate the humerus outward.
B. MUSCLES ON THE MEDIAL SURFACE OF THE SHOULDER.
=M. subscapularis= (Fig. 77, _a_).--A triangular mass from the subscapular fossa to the lesser tuberosity of the humerus.
_Origin_ (Fig. 78, _a_).--From the whole subscapular fossa except along the fusiform area for the attachment of the levator scapulæ and the serratus anterior near the vertebral border, and except over a quadrangular area about one centimeter long near the glenoid angle. The origin is by fleshy fibres directly from the periosteum except along two or three lines marked by oblique ridges. To these lines are attached tendinous fibres. At the glenoid border the area of origin sometimes occupies part or the whole of the surface of the fossa for the origin of the teres major, so that the teres arises from the fascia on the surface of the subscapularis. At the coracoid border some of the fibres may take origin from the adjacent fascia of the supraspinatus (Fig. 77, _d_).