_Insertion._--Mostly upon the outer surface of the spinodeltoideus (Fig. 75, _c_). The outer fibres are continued to the bone, especially at the lateral border of the muscle, and are inserted along a line ventrad of the line of insertion of the spinodeltoideus, and extending farther distally (Fig. 81, _g_). Some of the outer fibres pass into the brachialis (Fig. 80, _h_). _Relations._--Outer surface with the integument and the clavobrachial (Fig. 68, _e_). Inner surface with the infraspinatus (Fig. 75, _c_), teres minor (Fig. 80, _c_), spinodeltoid (Fig. 75, _e_), and caput laterale of the triceps (Fig. 75, _h_). _Action._--Like that of the spinodeltoid. =M. clavobrachialis= (Fig. 65, _k_; Fig. 68, _e_).--A flat, triangular muscle on the cranial surface of the shoulder, forming a direct continuation of the clavotrapezius (Fig. 68, _d_). These two are frequently described as constituting a single muscle, the cephalohumeral or cephalobrachial. (The clavobrachial is frequently given the name clavodeltoid; as its homology with the human clavodeltoid appears doubtful, it seems well to use the name clavobrachial, as proposed by Clasen.) [Illustration: FIG. 75.--MUSCLES ON THE LATERAL SURFACE OF THE ARM. _a_, M. supraspinatus; _b_, part of insertion of M. rhomboideus; _c_, M. infraspinatus; _d_, M. teres major; _e_, M. spinodeltoideus; _f_, M. acromiodeltoideus; _g_, caput longum of M. triceps brachii; _h_, caput laterale of M. triceps brachii; _i_, M. brachialis; _j_, M. biceps; _k_, M. brachioradialis; _l_, M. extensor carpi radialis longus; _m_, M. extensor communis digitorum (_m′_, tendon of same); _n_, M. extensor lateralis digitorum; (_n′_, tendon of same); _o_, M. extensor carpi ulnaris (_o′_, tendon of same); _p_, M. extensor indicis proprius; _q_, fifth head of M. flexor profundus digitorum; _r_, M. flexor carpi ulnaris. 1, vertebral border of the scapula; 2, spine of the scapula; 3, greater tuberosity of the humerus; 4, olecranon; 5, transverse ligament of the wrist.] _Origin._--Its superficial fibres are continuations of the clavotrapezius (Fig. 68, _d_); other fibres have origin from the clavicle and from a raphe laterad of the clavicle which is common to this muscle and the clavotrapezius. It passes distad along the cranial surface of the arm, growing narrower as it approaches the convexity of the elbow. _Insertion._--Eight to ten millimeters from the ulna it joins the brachialis muscle (Fig. 79, _i_) to be inserted with it by a flat tendon (Fig. 79, _i_; Fig. 87, _c_) upon a rough area on the medial surface of the ulna just distad of the semilunar notch, and about midway between the dorsal and ventral borders.