THE UPPER LIMB 3^5 



The cutaneous branches are three in number, and have been 

 already described. 



The ulnar nerve in the palm will be afterwards described. 



Median Nerve. — The median nerve lies at first in the anticubital 

 space, where it is placed on the inner side of the brachial and ulnar 

 arteries. On leaving the space it passes between the two heads of 

 the pronator radii teres, where it crosses the ulnar artery, the deep 

 head of that muscle intervening between the two. It then passes 

 beneath the radial origin of the flexor sublimis digitorum, and 

 descends under cover of that muscle in the middle line, until it 

 approaches the wrist. Here it escapes from beneath the muscle, 

 and lies between its tendons and that of the flexor carpi radialis, 

 where it parts with its palmar cutaneous branch. Thereafter it 

 passes under the anterior annular ligament into the palm, where 

 it will be afterwards described. The nerve is accompanied by the 

 median artery, which is a branch of the anterior interosseous near 

 its origin. 



Branches. — The branches of the nerve in the forearm are articular, 

 muscular, and cutaneous. 



The articular branches, one or two in number, enter the elbow- 

 joint on its anterior aspect. 



The muscular branches supply all the muscles on the front of 

 the forearm, except the flexor carpi ulnaris and the inner portion 

 of the flexor profundus digitorum. The branch, or branches, 

 to the pronator radii teres arise from the nerve before it passes 

 between the two heads of that muscle. The branches for the 

 flexor carpi radiahs, palmaris longus, and flexor sublimis digitorum 

 arise lower down. The flexor longus polUcis, outer portion of the 

 flexor profundus digitorum, and pronator quadratus are supplied 

 by the anterior interosseous branch. This long branch arises from 

 the median just below the neck of the radius, and it descends on 

 the front of the interosseous membrane, lying on the outer side of 

 the anterior interosseous artery, both being overlapped by the 

 contiguous borders of the flexor profundus digitorum and flexor 

 longus pollicis. On reaching the upper border of the pronator 

 quadratus the nerve passes beneath that muscle, and ends in two 

 branches, one of which enters the deep surface of the muscle, whilst 

 the other passes to supply the wrist-joint. The branch to the 

 outer portion of the flexor profundus digitorum arises high up, 

 and it communicates in the muscle with the branch of the ulnar 

 nerve to its inner portion. The anterior interosseous nerve in its 

 course furnishes an interosseous branch, which is distributed to the 

 interosseous membrane, and gives off medullary filaments which 

 accompany the medullary arteries of the radius and ulna. 



Third Layer of Muscles. — ^The muscles comprising the third or 

 deep layer are three in number, namely, the flexor profundus 

 digitorum, flexor longus pollicis, and pronator quadratus. 



I. Flexor Profundus Digitorum (flexor perforans) — Origin. — 

 (i) The upper three-fourths of the anterior surface of the ulna; 



