DISSECTION OF THE DOG 137 



A very small, variable muscular slip, sometimes difficult of demonstration, 

 leaves the humeral head of the deep flexor in the distal third of the forearm 

 and has been considered as homologous with the m. palmaris longus of man. 

 Its very thin tendon soon divides into two parts which accompany the common 

 tendon of the deep flexor into the palm, and terminate at the metacarpo- 

 phalangeal joint by uniting with the superficial flexor tendons of the third and 

 fourth digits. 



M. pronator quadratus. — The quadrate pronator muscle consists of 

 transverse fibres crossing from the radius to the ulna and filling the inter- 

 osseous space except at its ends. 



N. medianus. — The median nerve enters the forearm by passing between 

 the pronator teres and the proximal end of the radius. It follows the humeral 

 head of the deep flexor, and is related superficially to the flexor carpi radialis. 

 In the distal half of the forearm the nerve occupies a groove formed by the 

 humeral and radial heads of the deep flexor. Finally, crossing the flexor aspect 

 of the carpus, between the tendons of the superficial and deep flexors, it ends 

 as the volar metacarpal nerves (nn. metacarpei volares) of the first, second and 

 third digits, which gain these by coursing between the first and second, second 

 and third, and third and fourth metacarpal bones. 



The following arise from the median nerve : (1) A branch is contributed 

 to the pronator teres just before the median passes under this muscle. (2) 

 Under the pronator teres a large nerve arises for the supply of the radial flexor 

 of the carpus, the superficial flexor of the digits, and the humeral head 

 of the deep flexor. (3) A small branch accompanies the common interosseous 

 artery for a short distance, and terminates in the pronator quadratus and 

 radial head of the deep flexor of the digits. (4) A small branch supplies the 

 muscular slip which has been thought homologous with the m. palmaris 

 longus of man. 



N. ulnaris. — The ulnar nerve gains the forearm by traversing the interval 

 between the two heads of the flexor carpi ulnaris. It then travels towards the 

 carpus on the deep flexor of the digits (humeral head) and under cover of the 

 humeral head of the ulnar flexor of the carpus. Gaining the metacarpus by 

 crossing the medial aspect of the pisiform bone, the ulnar nerve ends by dividing 

 into a superficial and a deep branch. 



The branches of the nerve are as follows : (1) As the ulnar nerve is entering 

 the forearm it gives off a bunch of branches to the flexor carpi ulnaris and the 

 humeral and ulnar heads of the deep flexor of the digits. (2) A dorsal branch 

 (ramus dorsalis) arises in the proximal third of the forearm, becomes 

 superficial on the ulnar border of the limb just above the carpus, runs along 

 the lateral border of the carpus and metacarpus, and ends over the fifth digit. 

 (3) Terminal branches. Of these, the deep ramus (ramus profundus) 

 disappears from view almost at once, and must, therefore, be followed later. 

 The superficial branch (ramus superficialis) passes along the lateral border of 



