Part 40

Insertion (Fig. 87, c).--The dorsal portion of the depressed rough area on the lateral surface of the ulna just distad of the semilunar notch.

Relations.--Outer surface with the acromiodeltoid (Fig. 75, f), the caput laterale of the triceps (Fig. 75, h), the brachioradialis (Fig. 75, k), and the proximal end of the extensor carpi radialis longus (Fig. 75, l). Inner surface with the humerus. Medial edge with the pectoralis major (Fig. 65, l) and the biceps (Fig. 77, g).

Action.--Flexor of the antibrachium.

=M. triceps brachii.=--The triceps muscle of the cat, like that of man, is divisible (as its name indicates) into three main portions. These are a lateral portion (caput laterale), an intermediate or long portion (caput longum), and a medial portion (caput mediale). The first two correspond to the similarly named heads in man; the medial portion falls into a number of subdivisions whose homologues are uncertain.

a, M. supraspinatus; b, M. subscapularis; c, M. coracobrachialis; d, M. teres major (d′, its tendon); e, part of M. latissimus dorsi joining the teres major; f, cut end of M. pectoralis minor; g, long part of caput mediale of M. triceps brachii; h, intermediate part of caput mediale of M. triceps; i, M. brachialis (i′, its tendon); j, short part of caput mediale of M. triceps; k, cut end of M. clavobrachialis; l, l′, cut ends of M. biceps; m, M. brachioradialis; n, M. extensor carpi radialis longus; o, M. extensor carpi radialis brevis; p, fifth head of M. flexor profundus digitorum; q, first head of M. flexor profundus digitorum. 1, humerus; 2, olecranon; 3, medial epicondyle of humerus.]

=Caput laterale= (anconeus lateralis) (Fig. 75, h; Fig. 68, l).--The lateral portion is a flat muscle (most of it subcutaneous) on the lateral side of the brachium, connecting the proximal end of the humerus with the olecranon process of the ulna.

Origin (Fig. 81, h′).--By a flat tendon from the proximal portion of the deltoid ridge and the distal border of the teres minor tubercle.

Insertion (Fig. 86, c) by a thin, flat tendon into the lateral border of the dorsal surface of the ulna between a point opposite the distal margin of the semilunar notch and the proximal end of the olecranon.

Relations.--Lateral surface with the integument, and at the proximal end with the spinodeltoid and acromiodeltoid (Fig. 75, e and f). Medial surface with the brachialis (Fig. 75, i), the caput longum (g), the caput mediale, the brachioradialis (k), the anconeus (Fig. 80, l), and the origins of the extensor carpi radialis longus (Fig. 75, l), the extensor communis digitorum (m), and the extensor digitorum lateralis (n).

=Caput longum= (anconeus longus) (Fig. 75, g; Fig. 68, k; Fig. 77, i).--A prismatic, fusiform mass connecting the scapula with the olecranon.

Origin (Fig. 78, i) by a thick, flat tendon from a triangular area one or two centimeters long at the glenoid end of the scapula on the glenoid border. The base of the area is about one millimeter from the margin of the glenoid fossa.

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.

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).

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.