(2) The intermediate portion (anconeus internus) (Fig. 77, _k_; Fig. 79, _h_; Fig. 80, _j_). _Origin_ (Fig. 82, _g_) by fleshy fibres from a triangular area proximad of the middle of the dorsomedial surface of the humerus. The length of the area equals about one-fourth the length of the bone. Its apex points proximad and is almost continuous with the apex of the area of origin of the long portion. _Insertion_ (Fig. 87, _i_) by short tendon-fibres into the medial border of the ventral and proximal surfaces of the olecranon. It is connected with the tendon of the long portion. (3) Short portion (Fig. 79, _j_; Fig. 77, _l_). _Origin_ (Fig. 82, _h_) from the outer surface of the bony bar which encloses the supracondyloid foramen of the humerus, as far as the medial epicondyle. _Insertion_ (Fig. 87, _e_) by fleshy fibres into the medial border of the olecranon distad of the tuberosity for the insertion of the caput longum. _Relations_ of the caput mediale.--Lateral surface with the caput laterale (Fig. 75, _h_), the humerus, and the anconeus (Fig. 80, _l_). Dorsal surface with the caput longum (Fig. 77, _i_), the epitrochlearis (Fig. 65, _r_), and the teres major (Fig. 79, _d_). Ventral surface with the biceps (Fig. 77, _g_). _Action of the Triceps._--The entire triceps group forms a powerful extensor of the forearm. The short portion of the medial head tends also to rotate the arm outward, so as to supinate the hand. =M. anconeus= (Fig. 80, _l_).--A triangular muscle on the outside of the elbow-joint from the humerus to the ulna. _Origin_ (Fig. 83, _i_).--An irregularly triangular area at the distal end of the dorsal surface of the humerus. The area of origin is limited laterally by the sharp lateral supracondyloid ridge. It sometimes extends onto the lateral epicondyle. [Illustration: FIG. 81.--VENTRAL SURFACE OF HUMERUS, WITH THE AREAS OF ATTACHMENT OF MUSCLES. FIG. 82.--MEDIAL SIDE OF HUMERUS, WITH THE AREAS OF ATTACHMENT OF MUSCLES. FIG. 83.--DORSAL SURFACE OF THE LEFT HUMERUS, WITH THE AREAS OF ATTACHMENT OF MUSCLES. Fig. 81.--_a_, M. subscapularis; _b_, M. supraspinatus; _c_, Mm. teres major and latissimus dorsi; _d_, M. pectoralis minor; _e_, deep layer of M. pectoralis major; _f_, superficial layer of M. pectoralis major; _g_, M. acromiodeltoideus; _h_, M. spinodeltoideus; _h′_, caput laterale of M. triceps; _i_, M. brachialis; _j_, second portion of M. brachialis; _k_, M. extensor carpi radialis longus; _l_, M. extensor carpi radialis brevis; _m._ M. extensor communis digitorum; _n_, M. extensor lateralis digitorum; _o_, M. extensor carpi ulnaris; _p_, short portion of caput mediale of M. triceps; _q_, M. pronator teres; _r_, M. palmaris longus; _s_, third and fourth parts of M. flexor profundus digitorum; _t_, M. flexor carpi radialis; _u_, second head of M. flexor profundus digitorum.