260 FASCI.E AND MUSCLES OF THE HORSE 



lateral ligament. The long tendon (Lacertus fibrosus) is- thinner, blends with the 

 fascia of the forearm, and ends by fusing with the tendon of the extensor carpi 

 radialis. 



Relations. — Externally, the mastoido-humeralis and brachialis muscles; in- 

 ternally, the posterior deep pectoral and the superficial pectoral muscles; in front, 

 the anterior deep pectoral muscle; behind, the humerus, the coraco-brachialis mus- 

 cle, the anterior circumflex and anterior radial vessels, and the musculo-cutaneous 

 nerve. 



Blood-supply. — Branches of the brachial and anterior radial arteries. 



Nerve-supply. — Musculo-cutaneous nerve. 



2. Brachialis (Humeralis obliquus s. externus; brachiaHs anticus). — This 

 muscle occupies the musculo-spiral groove of the humerus. 



Origin. — The proximal third of the posterior surface of the humerus. 



Insertion. — The inner surface of the neck of the radius (under cover of the 

 lateral ligament) and the arciform ligament. 



Action. — To flex the elbow joint. 



Structure. — The peculiar spiral course of this muscle gave rise to the name 

 often applied to it — humeralis obliquus. Beginning on the posterior surface of the 

 shaft, close to the head of the humerus, it winds over the lateral surface, crosses the 

 biceps very obliquely, and finally reaches the inner side of the forearm by passing 

 between the biceps and the extensor carpi. It is entirely fleshy, with the exception 

 of its relatively slender tendon of insertion. 



Relations. — Externally the skin and fascia, the teres minor, deltoid, triceps 

 (lateral head), biceps, and mastoido-humeralis muscles. The anterior radial artery 

 crosses the deep face of the muscle in its distal third, and the radial nerve accom- 

 panies the muscle in the distal half of the musculo-spiral groove. 



Blood-supply. — Brachial artery. 



Nerve-supply. — Radial nerve. 



3. Tensor fascise antibrachii (Fig. 187)^ (Scapulo-ulnaris; long extensor 

 of the forearm; accessory anconeus of the latissimus dorsi). — This is a thin 

 muscle which lies on the inner surface of the triceps. 



Origin. — The tendon of insertion of the latissimus dorsi and the posterior 

 border of the scapula. 



Insertion. — (1) The fascia of the forearm; (2) a small eminence on the posterior 

 border of the olecranon. 



Action. — (1) To tense the fascia of the forearm and to extend the elbow 

 joint. 



Structure. — The origin consists of a very thin aponeurosis which blends with 

 those of the caput longuni and the latissimus dorsi. The muscular portion is 

 quite thin in its anterior part, somewhat thicker behind, and is narrower than the 

 aponeurotic origin. It is succecnled by an aponeurotic insertion, which ends chiefly 

 by blending with tiic fascia of the forearm a little below the elbow. There is, how- 

 ever, a small but constant tendinous attachment to the olecranon. 



Relations. — Externally, the panniculus, triceps (long and internal heads), 

 the inner and middle flexors of the carpus, and the ulnar vessels and nerve; in- 

 ternally, the latissinnis dorsi, serratus magnus, and ])osterior pectoral muscles. 



Blood-supply. — Subscapular, ulnar, and deep brachial arteries. 



N'ervc-su])})ly. — Radial nerve. 



4. Triceps brachii (Figs. 178, 179, 187) (Brachial triceps; triceps extensor 

 cubiti). — This, together with the ])receding muscle, constitutes the large muscular 



1 M'Failyean and Vauj:;lian tonn tliis muscle the scai)ulo-ulnaris, while Arloing and Lesbre 

 term it "Ancone accessoire du gi'^md dorsal." The above name seems to agree best with the 

 chief insertion and action, although it certainly arises largely from the tendon of insertion of 

 the latissimus dorsi. 



