=M. epitrochlearis= or extensor antibrachii longus (Fig. 65, _r_).--A thin, flat muscle on the inner or medial side of the brachium, from the lateral surface of the latissimus dorsi (Fig. 65, _q_) to the olecranon process of the ulna.
_Origin_ from the lateral or outer surface of the ventral border of the latissimus dorsi (Fig. 65, _q_) near the insertion of the cutaneus maximus. Fibres are often attached to the teres major and the pectoralis minor.
_Insertion_ by a flat tendon which is closely connected with that of the pectoantibrachialis (Fig. 65, _m_) and is continuous with the general antibrachial fascia, into the caudal border of the cutaneous (dorsal) surface of the olecranon process of the ulna.
_Relations._--Outer (medial) surface with the integument, the latissimus dorsi (Fig. 65, _q_), and the cutaneus maximus. Inner (lateral) surface with the biceps (Fig. 65, _t_), caput longum (Fig. 65, _s_), and caput mediale (Fig. 77, _j_, _k_) of the triceps.
_Action._--Extends the antibrachium and tends to supinate the hand by rotating the ulna.
=M. biceps brachii= (Fig. 77, _g_; Fig. 65, _t_).--A thick, fusiform muscle lying on the front (ventral) surface of the humerus.
_Origin_ (Fig. 76, _c_) by a strong, round tendon from the bicipital tubercle of the glenoid angle of the scapula, at its coracoid margin. (In man there is a second head--coracoid head--from the coracoid process.) The tendon passes through the capsule of the joint and then along the bicipital groove, which is converted into a canal by a strong ligament.
_Insertion_ by a rounded tendon (Fig. 87, _b_) on the bicipital tuberosity of the radius (Fig. 86, _k_).
_Relations._--The tendon of origin passes through the capsule of the joint, which is covered by a part of the pectoralis minor. The muscle is then spanned for the middle part of its course by the bicipital arch (Fig. 65, _t′_), a description of which is given below. Farther distad it is covered by the clavobrachial (Fig. 65, _k_) and epitrochlearis (Fig. 65, _r_). At its distal end (Fig. 79, _l′_) the muscle passes between the pronator teres on the radial side and the conjoined tendon of the brachialis and clavobrachial (Fig. 79, _i′_) on the other. The biceps lies throughout most of its length on the ventral surface of the humerus, and touches along the medial border of its inner surface the coracobrachialis (Fig. 77, _f_), the teres major, (Fig. 77, _c_), the intermediate portion of the caput mediale of the triceps (Fig. 77, _k_), and the short portion (Fig. 77, _l_) of the same. Its lateral border touches the pectoralis minor (Fig. 65, _o_) and the brachialis (Fig. 79, _i_).