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 accessorjr carpal 

 bone. It is chieflj' 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 inedial 

 epicondyle of the humerus and terminates near the carpus on a 

 tendon which passes downward outside of the carpal canal and 

 receives below the carpus two reinforcing bands, one from the 

 accessory carpal, the other from the sesamoid bone at the medial 

 side of the carpus. It divides distally into four branches, which 

 are inserted into the second phalanges of the second, third, 

 fourth, and fifth digits. 



The deep digital flexor has humeral, ulnar, and radial 



heads; the radial head arises from the medial border of the 



radius. They unite on a common tendon which passes down 



through the carpal canal, gives off a branch to the first digit, 



and divides into four branches. These perforate the tendons 



of the superficial flexor and are inserted into the third phalanges 



of the second to the fifth digits. The tendons are provided with 



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. 



Fig. 324. — Volar Mus- 

 cles OF Left Fore- 

 Paw OF Dog. 

 a. Abductor pol- 

 licia brevia et opponens 

 pollicis; b, flexor poUi- 

 cis brei'is; c, adductor 

 pollicis: d, adductor 

 digiti secundi; e, ad- 

 ductor digiti quinti; /, 

 flexor digiti quinti 

 brevis; g, abductor 

 digiti quinti; h, in- 

 terossei; 1, accessory 

 carpal bone; ^, first 

 digit; 3-G, sesamoids 

 of metacarpo-phalan- 

 geal joints. (Ellen- 

 berger-Baum, .\nat. d. 

 Hundes.) 



