_Insertion_ (Fig. 86, _b_).--The muscle ends in a thick tendon which passes over the bifurcated ventral end of the olecranon and is inserted upon the rounded tuberosity which forms the dorsal angle of the olecranon.
_Relations._--Lateral surface with the caput laterale (Fig. 75, _h_), a portion of the caput mediale (Fig. 77, _j_ and _k_), the spinodeltoid (Fig. 75, _e_), the infraspinatus (Fig. 75, _c_), and the integument. Medial surface with the epitrochlearis (Fig. 65, _r_) and the conjoined portions of the latissimus dorsi and teres major (Fig. 79, _d′_). Ventral border with the caput mediale (Fig. 77, _j_ and _k_).
=Caput mediale.=--The medial head consists of three portions (Fig. 79, _g_, _h_, _j_).
(1) The long portion (anconeus posterior) (Fig. 77, _j_; Fig. 79, _g_; Fig. 80, _f_).
_Origin_ (Fig. 83, _e_) from a triangular area on the dorsal surface of the humeral shaft. The base of the area is against the articular head, and its apex about one-sixth the length of the humerus from the head. It is between the coracobrachialis and the lateral head of the triceps.
[Illustration: FIG. 80.--DEEP MUSCLES ON THE LATERAL SURFACE OF THE HUMERUS.
_a_, part of M. supraspinatus; _b_, part of M. infraspinatus; _c_, M. teres minor; _d_, M. teres major; _e_, part of M. latissimus dorsi joining M. teres major; _f_, long part of caput mediale of M. triceps brachii; _g_, cut insertion of M. acromiodeltoideus; _h_, M. brachialis; _i_, M. brachioradialis; _j_, intermediate part of caput mediale of M. triceps brachii; _k_, M. extensor carpi radialis longus; _l_, M. anconeus; _m_, M. extensor communis digitorum. 1, great tuberosity of humerus; 2, 3, superficial radial and dorsal interosseous branches, respectively, of the radial nerve.]
_Insertion_ (Fig. 86, _a_).--The muscle ends in a long, slender tendon which passes through the furrow on the ventral angle of the olecranon and is inserted into an oblique ridge which forms the dorsal limit of the furrow. The tendon is separated from the floor of the furrow by a synovial bursa.
(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.