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.
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).