326 THE MUSCLES. 



its course between the two tendons of the extensors of the phalanges to the near 

 fetlock, where it becomes mixed with that of the lateral extensor, a little above 

 the first phalanx. 



The muscle of Thiernesse is smaller than that of Phillips, and situated at its 

 inner side. It arises, in front of the transverse ligament of the ulna, by a 

 muscular portion, becomes thinner as it descends, and terminates by a fine 

 tendon which is confounded with that of the common extensor, towards the 

 lower third of the forearm.) 



4. Lateral Extensor of the Phalanges (Extensor Suffraginis) 

 (Figs. 179, 16 ; 182, 13). 



Synonyms. — Cubito or radialis-prephalangeus, according to Girard. The extensor minimi 

 digiti of Man. 



Direction — Situation — Extent — Form — Structure. — A small vertical muscle, 

 situated at the external side of the forearm, between the preceding and the 

 external flexor of the metacarpus, and formed of a fleshy body and a tendon. 

 The body, not very considerable, and flattened, extends from the upper extremity 

 of the radius to its lower fourth. The tendon (Fig. 179, 16'), at first rounded, 

 then flattened, reaches the gliding groove which divides the external inferior 

 tuberosity of the radius into two portions, passes to the external side of the 

 carpus, crossing the lateral ligament common to the articulations of this region, 

 and arrives at the anterior surface of the principal metacarpal bone, where it 

 receives the small tendinous branch detached from the anterior extensor, as well 

 as a strong fibrous band coming from the external side of the carpus (Fig. 179, 

 17). Afterwards, descending alongside the external border of the principal 

 tendon of its congener, and united to it by a fibrous fascia, it gains the articula- 

 tion of the fetlock, and expanding, terminates at the upper extremity of the first 

 phalanx. 



Attachments. — 1. By its muscular body, to the external tuberosity of the 

 radius, the external ligament of the elbow articulation, and to the bodies of the 

 two bones of the forearm — origin. 2. By the inferior extremity of its tendon, 

 to the capsule of the metacarpo-phalangeal articulation, and in front of the 

 superior extremity of the first phalanx — termination. 



Relations. — Its muscular portion, enveloped in a special aponeurotic sheath, 

 responds : in front, to the anterior extensor of the phalanges ; behind, to the 

 external flexor of the metacarpus, and the perforatus and perforans muscles ; 

 outwards, to the antibrachial aponeurosis. The tendon, surrounded by a vaginal 

 synovial sheath, in passing over the carpus, covers, beyond the knee, the anterior 

 aspect of the metacarpus and the anterior ligament of the metacarpo-phalangeal 

 articulation, over which it glides by means of a small vesicular synovial bursa. 

 It is covered by a slight fascia, which separates it from the skin, and which is 

 also spread over the tendon of the anterior extensor. 



Action. — This muscle is an extensor of the digit, and also concurs in the 

 extension of the entire foot on the forearm. 



In the Ass, this muscle is proportionately much smaller than in the Horse. 



B. Posterior Antibrachial Region. 



This is composed of five flexor muscles grouped vertically behind the bones 

 of the forearm. Three are situated superficially, and act on the whole of the 



