EXTENSOR DIVISION 309 
elbow joint, the shaft of the ulna, the lateral border of the radius, and the inter- 
muscular septum. 
Insertion.—An eminence on the 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 
Extensor carpi radialis 
Common digital extensor 
Cutaneous branch of mus- 
culo-cutaneous nerve 
Cephalic vein 
Extensor carpi obliquus 
Intermuscular septum 
Lateral digital extensor (Median nerne 
Intermuscular septum 
Flexor carpi radialis 
Deep digital fleror 
(humeral head) 
Ulnaris lateralis 
Flexor carpi ulnaris 
Deep digital flexor 
(ulnar head) 
Ulnar vessels and nerve Dain domaine: 
Fic. 280 —Cross-secrion oF Lerr 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, branches 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 
