310 FASCLE AND MUSCLES OF THE HORSE 
interosseous artery; behind, the lateral flexor of the carpus and the deep flexor of 
the digit. 
Blood-supply.—Interosseous artery. 
Nerve-supply.—Radial nerve. 
4. Extensor carpi obliquus (M. abductor pollicis longus et extensor pollicis 
brevis)."—This is a small muscle which curves obliquely over the distal half of the 
radius and the carpus. 
Origin.—The lateral border and adjacent part of the dorsal surface of the 
radius (the attachment area beginning at a point above the middle of the bone and 
extending down to its distal fourth). 
Insertion.—The head of the medial (second) metacarpal bone. 
Action.—To extend the carpal joint. 
Structure.—The muscle is pennate and has a flat belly which curves downward, 
forward, and medially over the distal part of the radius. The tendon continues 
the direction of the muscle, and passes over the tendon of the extensor carpi radialis; 
it then occupies the oblique groove at the distal end of the radius, and crosses the 
medial face of the carpus. It is provided with a synovial sheath. 
Relations.—Superficially, the skin and fascia, the lateral extensor, and the 
common extensor; deeply, the radius, the extensor carpi radialis, the carpal joint 
capsule, and the medial ligament of the carpus. 
Blood-supply.—Interosseous and anterior radial arteries. 
Nerve-supply.— Radial nerve. 
B. FLEXOR DIVISION 
1. Flexor carpi radialis (or medial flexor of the carpus).2—This muscle lies on 
the medial surface of the forearm, behind the border of the radius. 
Origin.—The medial epicondyle of the humerus, below and behind the col- 
lateral ligament. 
Insertion.—The proximal end of the medial (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 sueceeded by a 
somewhat flattened, fusiform belly. The tendon of insertion begins near the distal 
fourth of the radius and descends in a canal in the transverse carpal ligament. It 
is provided with a synovial sheath which begins two or three inches (ca. 5-8 em.) 
above the carpus and extends almost to the insertion of the tendon. 
Relations.—Superficially, the skin and fascia, the posterior superficial pectoral, 
and the tensor fascie antibrachii; deeply, the elbow joint, the radius, the deep 
flexor, the flexor carpi ulnaris, the median vessels, and the median nerve. At the 
elbow the artery and nerve lie in front of the muscle, but below they dip beneath it. 
Blood-supply.—Median artery. 
Nerve-supply.— Median nerve. 
On removing the deep fascia on the medial surface of the elbow the student may notice a 
small muscle lying along the collateral ligament. This.is the pronator teres, which is usually 
not present or a mere vestige in the horse. It arises by a small, flat tendon from the medial epi- 
condyle of the humerus, and is inserted into the medial ligament of the elbow. On account of its 
small size and the fact that the forearm is fixed in the position of pronation, the muscle can have 
no appreciable function. It is usually represented by a tendinous band. 
2. Flexor carpi ulnaris (or middle flexor of the carpus).*—This muscle lies on the 
medial and posterior aspect of the forearm, partly under, partly behind, the preced- 
ing muscle. It arises by two heads—humeral and ulnar. 
! Also known as the extensor metacarpi obliquus. 
2 Also known as the flexor carpi s. metacarpi internus or radialis volaris. 
* Also known as the flexor carpi (s. metacarpi) medius or ulnaris medialis. 
