MUSCLES OF THE ANTEEWH LIMBS. 325 



muscular portion extends from the inferior extremity of the humerus to above 

 the lower third of the radius ; it is fusiform in shape, intersected by aponeurotic 

 layers, and bifid at its superior extremity.^ The tendinous portion forms two 

 unequal cords, which succeed the two terminal branches of the muscular part, 

 and lie close to each other. These two cords enter the most external of the 

 three grooves in front of the inferior extremity of the radius, and reach the 

 anterior face of the carpal capsular ligament, against which they are maintained 

 by au annular ligamentous apparatus. After passing from beneath this ring, the 

 smallest, which is the most external, joins the tendon of the lateral extensor (Fig. 

 179, 15). The principal branch (Fig. 179, 14') continues its course on the 

 anterior aspect of the middle metacarpal bone and articulation of the fetlock, 

 until it arrives in front of the digit ; here it terminates on the os pedis, after 

 widening in a remarkable manner, and after receiving, laterally, at the middle of 

 the first phalanx, a reinforcing band which appears to be given off from the 

 inferior extremity of the suspensory ligament of the fetlock. 



Attachments. — It has its fixed attachment by the superior extremity of its 

 muscular body. 1. Below the crest that limits, posteriorly, the musculo- 

 spiral groove 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 process 

 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. 



Relations. — The muscular portion, covered by the antibrachial aponeurosis, 

 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 bone, to which it is intimately attached by its upper half ; 

 behind, to the lateral extensor of the phalanges. The tendinous cords cover the 

 difTerent 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 principal 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 i 

 of the entire foot on the forearm. i 



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

 extensor, have been particularly described by Thiemesse and PhiUips, and named 

 after these authors. 



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

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

 superior tuberosity of the radius ; it is directed obliquely 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 



' This division, which has been nuticed by several writers, has not been shown in Fig. 179 

 This is a mistake, :is it is constantly present. 



