_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_). _Action._--Flexes the forearm, and tends to supinate the hand. =The bicipital arch= (Fig. 65, _t′_) is a tendinous arch formed over the biceps muscle. Its outer or lateral pillar is formed by the tendon of the pectoralis minor (_o_), to which may be added part of the latissimus (_q_) tendon. Its inner or medial pillar is formed by the conjoined tendon of the teres major and latissimus dorsi (Fig. 79, _d′_), while the xiphihumeralis (Fig. 65, _p_), cutaneus maximus (Fig. 62, _b_), and epitrochlearis (Fig. 65, _r_) are connected with one or the other pillar or with the muscles composing them. The caudal portion of the deep layer of the pectoralis major (Fig. 65, _l_) may be connected with the inner pillar. =M. brachialis= (Fig. 79, _i_; Fig. 75, _i_).--From the lateral surface of the humerus to the ulna.