FLEXOR DIVISION 313 



the forearm the ulnar vessels and nerve lie between the lateral edge of this muscle 

 and the lateral flexor of the carpus. 



Blood-supply. — Ulnar and median arteries. 



Nerve-supply. — Ulnar and median nerves. 



3. Ulnaris lateralis (or lateral flexor of the carpus).^ — This muscle lies on the 

 lateral face of the forearm, behind the lateral extensor of the digit. 



Origin. — The lateral epicondyle of the humerus, behind and below the lateral 

 ligament. 



Insertion. — (1) The lateral surface and proximal border of the accessory carpal 

 bone; (2) the proximal extremity of the lateral (fourth) metacarpal bone. 



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



Structure. — The belly of the muscle is flattened and is intersected by a good 

 deal of tendinous tissue. There are two tendons of insertion. The short tendon 

 is inserted into the accessory carpal bone. The long tendon is detached just above 

 the carpus; it is smaller and rounded; it passes downward and a little forward 

 through a groove on the lateral surface of the accessory carpal bone, enveloped by 

 a synovial sheath, to reach its insertion on the lateral metacarpal bone. A synovial 

 pouch lies under the origin of the muscle at the elbow joint, with the cavity of 

 which it communicates. 



Relations. — Superficially, the skin, fascia, and cutaneous branches of the ulnar 

 nerve; deeply, the elbow joint, the ulna, and the flexors of the digit; in front, the 

 lateral extensor of the digit; behind, the middle flexor of the carpus, the ulnar head 

 of the deep flexor, and the ulnar vessels and nerve. 



Blood-supply. — Interosseous, ulnar, and median arteries. 



Nerve-supply. — Radial nerve. 



4. Superficial digital flexor^ (M. flexor digitalis superficialis). — This muscle is 

 situated in the middle of the flexor group, chiefly under cover of the middle flexor 

 of the carpus. 



Origin. — (1) The medial epicondyle of the humerus; (2) a ridge on the pos- 

 terior surface of the radius, below its middle and near the medial border. 



Insertion. — (1) The eminences on the proximal extremity of the second phalanx, 

 behind the collateral ligaments; (2) the distal extremity of the first phalanx, also 

 behind the collateral ligaments. 



Action. — To flex the digit and carpus and to extend the elbow. 



Structure. — The fleshy part of the muscle is the humeral head (Caput humerale) ; 

 it takes origin from the humerus. The radial head (Caput tendineum) consists of 

 a strong fibrous band, usually termed the radial or superior check ligament, which 

 fuses with the tendon near the carpus. The belly of the muscle is intersected by 

 tendinous strands, and fuses more or less with that of the deep flexor, from which 

 it is therefore somewhat difficult to separate. Near the carpus it is succeeded by a 

 strong, thick tendon which passes down through the carpal canal and is enveloped 

 by a synovial sheath, in common with the deep flexor. This, the carpal sheath 

 (Vagina carpea), begins three or four inches (8-10 cm.) above the carpus, and ex- 

 tends downward nearly to the middle of the metacarpus. Below the carpus the 

 tendon becomes flattened and broader and at the fetlock it widens greatly. Near 

 the fetlock it forms a ring through which the tendon of the deep flexor passes (Fig. 

 286). Here the two tendons are bound down in the sesamoid groove by the volar 

 annular ligament, which fuses more or less with the superficial flexor tendon. At 

 the distal end of the first phalanx the tendon divides into two branches which di- 

 verge to reach their points of insertion, and between these branches the tendon of 



1 Also known as the flexor carpi (s. metaoarpi) externus or extensor carpi ulnaris. Morpho- 

 logically it belongs to the extensor group. 



^ Also commonly known as the flexor perforatus or superficial flexor of the phalanges. 



