264 THE MUSCLES. 



reinforcing band which appears to be given off from the inferior extremity 

 of the suspensory ligament of the fetlock. 



Attachments. — The anterior extensor of the phalanges has its fixed attach- 

 ment by the superior extremity of its muscular body : 1, Below the crest 

 that limits, posteriorly, the furrow of torsion of the humerus ; 2, In front 

 of the inferior extremity of the humerus ; 3, To the anterior border of the 

 external ligament of the elbow joint; 4, To the external and superior 

 tuberosity of the radius ; 5, To the external border of that bone. Its 

 principal tendon is inserted into the pyramidal eminence of the third phalanx, 

 after being successively attached to the capsular ligament of the fetlock 

 joint and the anterior surfaces of the first two phalanges. • 



Helations. — The muscular portion, covered by the antibrachial aponeu- 

 rosis, covers the articulation of the elbow, the anterior face of the radius, 

 and the oblique extensor of the metacarpus ; it responds, in front, to the 

 anterior extensor of the same ray, to which it is intimately attached by its 

 upper half ; behind, to the lateral extensor of the phalanges. The tendinous 

 cords cover the different parts already enumerated in describing the course 

 of the muscle — that is, the anterior face of the radius, the carpal joints, the 

 principal metacarpal bone, the articulation of the fetlock, and the first two 

 phalanges. A vaginal synovial membrane envelops them at the knee, to 

 facilitate their gliding in the radial groove and on the anterior aspect of 

 the capsular ligament of the carpus ; while the inner surface of the prin- 

 cipal tendon is covered, in front of the fetlock, by a small vesicular 

 capsule, and still lower by the synovial membranes of the two inter- 

 phalangeal articulations. 



Action. — This muscle extends the third phalanx on the second, that on 

 the first, and this again on the metacarpal bone. It may also concur in the 

 extension of the entire foot on tie fore-arm. 



(Two small muscles, which should be only considered as heads of this 

 anterior extensor, have been particularly described by Thiernesse and 

 Phillips, and named after these authors. 



The muscle of Phillips, according to Leyh, is long and thin ; it commences 

 on the lateral external ligament of the ulnar articulation and the external 

 superior tuberosity of the radius ; it is directed ebliquely downwards and 

 forwards, lying beside the muscular portion of the common extensor. 

 Towards the middle and outer aspect of the radius, it gives off a small 

 tendon, which passes in the same sheath as the preceding, in front of the 

 carpus, and continues its course between the two tendons of the extensors 

 of the phalanges to near the fetlock, where it becomes confounded 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 ths 

 lower third of the fore-arm.) 



4. Lateral Extensor of the Phalanges. (Pigs. 119, 16 ; 122, 13.) 



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

 mmimi digiti of Man. (Extensor suffraginis—PercivaU.) 



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

 situated at the external side of the fore-arm, between the preceding and 

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



