THE BRACHIAL PLEXUS 361 



annular ligament, and supplies the skin over the ball of the 

 thumb and the palm. It communicates with branches of the 

 ulnar and external cutaneous nerves. 



3. In the palm the nerve lies on the flexor tendons, 

 covered by the annular ligament, and becomes larger and 

 reddish in color. It divides into two branches the external, 

 supplying some of the muscles of the thumb and digital branches 

 to the thumb and index finger; and the internal, supplying 

 digital nerves to the index, middle, and ring fingers. 



The muscular branches supply the abductor, opponens, 

 and outer head of the flexor brevis pollicis. The first digital, 

 with the second, supplies the thumb, the former joining a 

 branch of the radial. The third, along the radial side of the 

 index finger, supplies it and the first lumbricalis. The fourth 

 supplies the adjacent sides of the index and middle fingers 

 and the second lumbricalis. The fifth, to the adjacent sides 

 of the middle and ring fingers, joins a branch of the ulnar. 

 Each digital nerve divides at the tip of the finger into a branch 

 to the pulp and one to the matrix of the nail. At the base 

 of the first phalanx each sends a branch to the back of the 

 second and third phalanges. 



The ulnar nerve from the inner cord runs internal to the 

 axillary and brachial arteries as far as the middle of the arm. 

 It then passes on the inner head of the triceps to the groove 

 between the olecranon and internal condyle with the inferior 

 profunda artery, and runs between the two heads of the flexor 

 carpi ulnaris with the posterior ulnar recurrent artery, lying 

 beneath the muscle above and to the radial side of it below. 

 In the lower two-thirds of the forearm the ulnar artery is 

 external. The nerve then crosses the annular ligament between 

 the artery and pisiform bone, and divides into a superficial 

 and a deep branch. 



BRANCHES. 1. In the arm, none. 



2. In the forearm, several articular to the elbow. Muscular, 

 to the flexor carpi ulnaris and inner half of the flexor profundus. 

 Two cutaneous by a common trunk. One joins a branch of 

 the internal cutaneous, and the other, the palmar cutaneous, 

 runs on the ulnar artery to the palm, joining branches of the 

 median nerve. 



The dorsal cutaneous comes off about two inches above the 

 wrist, runs backward beneath the flexor carpi ulnaris, and 



