374 THE MUSCLES OF THE DOG 
its tendon divides at or near the carpus into two branches, which are inserted into 
the third phalanges of the third and fourth digits, blending with the corresponding 
tendons of the common extensor. The posterior muscle is the extensor of the fifth 
digit (M. extensor digiti quinti); its tendon fuses with that of the common extensor 
for the fifth digit. 
The ulnaris lateralis or extensor carpi ulnaris is a large flat muscle which lies 
on the lateral surface of the ulna. It arises on the lateral epicondyle of the humerus, 
and is inserted into the proximal end of the fifth metacarpal and the accessory carpal 
bone. It is chiefly an abductor of the paw. 
The flexor carpi ulnaris consists of two quite distinct heads. The larger 
humeral head arises on the medial epicondyle, while the smaller, 
superficial ulnar head arises on the posterior border of the ulna. 
The tendons of the two end on the accessory carpal bone and 
have a bursa between them. 
The flexor carpi radialis arises on the medial epicondyle of 
the humerus and is inserted by a bifid tendon into the second 
and third metacarpal bones. 
The tendons of the foregoing eight muscles are provided 
with synovial sheaths at the carpus. 
The pronator teres is a fusiform muscle, which is situated 
superficially on the proximal part of the medial border of the 
radius. It arises on the medial epicondyle of the humerus, and 
is inserted into the dorsal surface and medial border of the radius 
almost half way to the carpus. It is related deeply to the radial 
vessels, the median nerve, and the tendon of the biceps. Its 
action is to flex the elbow and rotate the forearm inward (pro- 
nation). 
The superficial digital flexor is situated superficially on 
, the medio-volar surface of the forearm. It arises on the medial 
ae ee epicondyle of the humerus and terminates near the carpus on a 
Paw or Dos. tendon which passes downward outside of the carpal canal and 
a, Abduetor pole receives below the carpus two reinforcing bands, one from the 
eee yee accessory carpal, the other from the sesamoid bone at the medial 
cis brevis: c, adductor Slide of the carpus. It divides distally into four branches, which 
pollicis; d, adduetor are inserted into the second phalanges of the second, third, 
See ian quini ,, fourth, and fifth digits. 
flexor digiti quinti The deep digital flexor has humeral, ulnar, and radial 
brevis; g, abductor heads; the radial head arises from the medial border of the 
digiti quinti; h, in- : =i : ; : ; 5 
terossei: 1, accessory acius. They unite on a common tendon which passes down 
carpal bone; 2, first through the carpal canal, gives off a branch to the first digit, 
ee em eee and divides into four branches. These perforate the tendons 
eal Ag ota of the superficial flexor and are inserted into the third phalanges 
berzer-Baum, Anat. d. of the second to the fifth digits. The tendons are provided with 
Bede) synovial sheaths from the middle of the metacarpus downward, 
and are held in place by three digital annular ligaments. 
The palmaris longus! is a small muscle which arises from the deep digital 
flexor below the middle of the forearm, and ends by two tendons which unite with 
those of the superficial flexor for the third and fourth digits. 
The supinator is a short, flat, fusiform muscle which arises from the front of 
the lateral epicondyle of the humerus with the lateral ligament, and from the lateral 
prominence of the head of the radius, and is inserted into the proximal fourth of the 
1 The homology here is doubtful. Sussdorf regards the ulnar head of the deep digital flexor 
as the homologue of the palmaris longus of man, while Alexais considers that the latter is repre- 
sented by the superficial digital flexor. 
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