136 DISSECTION OF THE DOG 



At the carpus three strong fibrous bands join the superficial flexor tendon. 

 The first passes from the medial border of the carpus ; the second is derived 

 from the pisiform bone ; and the third from the sesamoid at the medial side 

 of the carpus connected with the tendon of the abductor pollicis longus. 



In the palm the flexor tendons are contained in flexor sheaths comparable 

 to those of the pes. 



Slips to the callosities of the digits leave the tendons on a level with the 

 metacarpo-phalangeal joint. Close to the carpus a separate tendinous and 

 feebly muscular slip branches off from the lateral border of the flexor tendon of 

 the fifth digit and ends in a transverse thickening of the flexor sheath opposite 

 the metacarpo-phalangeal joint. 



M. flexor cabpi ulnaris. — This really consists of two separate muscles. 

 The more superficial and the weaker head (caput ulnare) arises from the 

 olecranon and is inserted into the pisiform bone by a thin flattened tendon 

 which begins about the middle of the forearm. The deep, strong humeral 

 head (caput humerale) lies mainly under cover of the flexor digitorum sublimis. 

 It arises from the medial epicondyle of the humerus, and is inserted into the 

 pisiform bone by a very short, strong tendon. 



The humeral head is anterior to the ulnar at its origin ; but the ulnar head 

 passes obliquely across the lateral surface of the humeral head, with the result 

 that the small ulnar tendon is inserted into the pisiform in front of the stout 

 humeral tendon. At their insertion a small synovial bursa intervenes between 

 the two tendons. 



The deep layer of muscles consists of mm. flexor digitorum profundus and 

 pronator quadratus. 



Dissection. — In order to follow the deep flexor tendons it is necessary to cut 

 across the superficial flexor about the end of its fleshy belly. Liberate the 

 tendon from its accessory slips derived from the carpus, and turn it 

 downwards. At the carpus the superficial and deep flexor tendons are 

 separated by a strong transverse band passing from the pisiform to the 

 medial border of the carpus. This must be divided. Reflect the two 

 heads of the flexor carpi ulnaris. 



M. flexor digitorum profundus. — The deep flexor of the digits has 

 three independent fleshy bellies. The largest, the humeral head, arises from 

 the medial epicondyle of the humerus. The ulnar head — second in point of 

 size — has origin from the proximal half of the ulna. The radial head is slender 

 and springs from the middle two-fourths of the medial border of the radius. 

 The tendons of the three heads join a short distance proximal to the carpus. 

 The common tendon passes down the flexor side of the carpus, and, arriving 

 in the palm, divides into four parts, each inserted into the terminal phalanx 

 of a digit. 



