FLEXOR DIVISION 



267 



Nerve-supplij. — Radial nerve. 



4. Extensor carpi obliquus (M. abductor pollicis longus et extensor pollicis 

 brevis; oblique extensor of the metacarpus; extensor metacarpi obliquus). — This 

 is a small muscle which curves ol)liquely over the distal half of the radius and the 

 carpus. 



Origin. — The external border and adjacent part of the anterior surface of the 

 radius (the attachment area beginning at a point above the middle of the bone and 

 extending down to its lower fourth). 



Insertion.— The head of the inner (second) metacarpal bone. 



Action. — To extend the carpal joint. 



Structure. — The muscle is pennate and has a flat belly which curves downward, 

 forward, and inward over the distal part of the radius. The tendon continues the 

 direction of the muscle, crossing obliquely over the tendon of the extensor 

 carpi radialis; it then occupies the oblique groove at the distal end of the radius, 

 and crosses the inner face of the carpus. It is provided with a synovial sheath. 



Fig. 192. — Cross-sectiox of Middle of Rigitt Forearm of Horse 

 a. Accessory cephalic vein; 6, cutaneous branch of median nerve; c, extensor carpi obliquus; d, posterior 

 radial artery; e, satellite vein; /, median nerve; g, g' , ulnar vessels; h, ulnar nerve; i, cephalic vein; k, tendon of 

 ulnar head of deep flexor; /, interosseous artery; m, extensor carpi radialis; n, anterior digital extensor; u, lateral 

 digital extensor; p, flexor carjji externus; q, q, q, humeral heads of deep digital flexor; r, radial head of same; s, 

 superficial digital flexor; /, flexor carpi medius; w, flexor carpi internus; v, radius; w, skin; x, anterior radial 

 artery. (After Ellenberger, in Leisering's Atlas.) 



Relations. — Superficially, the skin and fascia, the lateral extensor, and the 

 common extensor; deeply, the radius, the extensor carpi radialis, the carpal cap- 

 sule, and the internal lateral ligament. 



Blood-supplij. — Interosseous and anterior radial arteries. 



Nerve-supply. — Radial nerve. 



B. Flexor Division 



1. Flexor carpi internus (AI. flexor carpi radialis s. radialis volaris; internal 

 flexor of the metacarpus). — This muscle hes on the inner surface of the forearm, 

 immediately behind the inner border of the radius. 



Origin. — The flexor (internal) epicondyle of the humerus, below and behind 

 the lateral ligament. 



Insertion. — The proximal end of the internal (second) metacarpal bone. 



Action. — To flex the carpal joint and to extend the elbow. 



Structure. — The muscle has a short tendon of origin, which is succeeded by a 

 somewhat flattened, fusiform belly. The tendon of insertion begins near the distal 

 fourth of the radius. It is provided with a synovial sheath which begins two or 



