EXTENSOR DIVISION 



309 



elbow joint, the shaft of the ulna, the lateral border of the radius, and the inter- 

 muscular septum. 



Lisertion.— An eminence on t^e front of the proximal extremity of the first 

 phalanx. 



Action. — To extend the digit and carpus. 



Structure.— The muscle is pennate, and is enclosed in a sheath formed by the 

 deep fascia, from which many fibers arise. The belly is thin and fusiform and 

 terminates at the distal third of the forearm. From here the tendon (at first 

 small and round) passes downward through the groove on the lateral tuberosity 

 of the distal end of the radius, then over the carpus, and, gradually inclining toward 



Intermuscular septum 



Coinmon digital extensor 



Extenscyr carpi obliquus 



Intermuscular septum 



Lateral digital exte7isor 

 Intermuscular septum 



Deep digital flexor 

 (humeral head) 



Ulnaris lateralis 



Deep digital flexor 

 {ulnar head) 



Ulnar 



Extensor carpi radialis 



a.;\ Cutaneous branch of mus- 

 ^\ culo-cutaneous nerve 

 Cephalic vein 



Median nerve 

 Flexor carpi radialis 



Flexor carpi ulnaris 



Superficial digital flexor 



Fig. 280. — Cross-section of Left Forearm of Horse. 



Section is cut a little above middle of region and the figure is a proximal view. 



1, Median artery and satellite veins; 2, 3, branciiea of deep brachial and anterior radial vessels; 4, dorsal interosseous 



vessels. 



the front, but not reaching the middle line of the limb, it passes over the meta- 

 carpus and fetlock to its insertion. Two synovial membranes occur in connection 

 with the tendon. A synovial sheath envelops the tendon, beginning about three 

 inches (ca. 6-8 cm.) above the carpus, and reaching to the proximal end of the 

 metacarpus. At the fetlock a small bursa lies between the tendon and the joint 

 capsule, but otherwise the tendon is adherent to the capsule. The tendon becomes 

 flat and much larger below the carpus, having received the tendon of the radial 

 head of the common extensor and a strong band from the accessory carpal bone. 



Relations. — Superficially, the skin and fascia; deeply, the lateral face of the 

 radius and ulna; in front, the common extensor, the oblique extensor, and the 



