794 THE yERVOUS SYSTEM 



described later on (page 797). Tlie inner branch communicates with the ulnar 

 nerve and divides to supply the adjacent sides of the middle and ring lingers. 



As the branches of the median nerve pass downwards in tlie palm of the hand, they cross the 

 deej) or posterior suifaee of the supertieial palmar arch. Tliis ivlation to the art dies is reversed 

 in the fingers, where the digital arteries are i)laccd behind the nerves. As each digital nerve 

 pursues its cour.se along the margin of the corresponding finger, it gives off" twigs to the dorsum 

 of the finger, which supply the skin on the dorsum of the second and third phalanges, particu- 

 larly stout twigs passing to sui)i)ly the matrix of the nail. Each nerve terminates in branches to 

 the pulp of the finger, and on these terminal branches as well as on the more j^roximal twigs to 

 the volar aspect of the fingers, ovoid bodies, about the size of millet seeds, are developed. These 

 bodies are called Pacinian corpuscles, and are one of the forms of sensory nerve-terminations. 



(6) The ulnar nerve is the largest branch of the inner cord of the brachial 

 plexus, and is derived from the eighth cervical aiul lirst thoracic nerves. It runs 

 downwards between the axillary artery and the vein, posteriorly, and preserves the 

 same relation to the brachial artery for the upper third of the arm. It then 

 diverges from the brachial artery at an acute angle, and accompanies the inferior 

 profunda artery through the internal muscular septum and downwards upon the 

 inner head of the triceps to the interval between the internal condyle of the humerus 

 and the olecranon processes of the ulna. In this course it is jjlaced under cover of 

 the deep fascia. It then passes between the two heads of the flexor carpi ulnaris, 

 comes into relation with the posterior ulnar recurrent artery, and runs downwards 

 under cover of the flexor carpi ulnaris muscle, 1;)etween it and the flexor profundus 

 digitorum, to reach the wrist. At the junction of the upper and middle thirds of 

 the forearm it is joined, at an acute angle, l\v the ulnar artery, and runs jiarallel to 

 the inner side of that vessel in the middle and lower two-thirds of the forearm 

 under cover of the flexor carpi ulnaris, and between that muscle and the flexor 

 sublimis digitorum. Just above the wrist it pierces the deep fascia, enters the 

 hand by crossing the superficial surface of the anterior annular ligament close to the 

 radial border of the pisiform bone, and terminates 1)V bifurcating into a superficial 

 and a deep division. 



Branches. — The ulnar reseml)les the median nerve in not furnishing any 

 branches to the upper arm. As it passes lietween the olecranon process and the 

 internal condyle, it gives off two or three fine filaments to the elbow-joint. In the 

 forearm it supplies the flexor carpi ulnaris and the inner portion of the flexor 

 profundus digitorum, and gives off the three cutaneous branches. In the hand it 

 supplies the integument of the hypothenar eminence, the little finger and half of 

 the ring finger and part of the dorsum; it also gives twigs to the palm and supplies 

 the short intrinsic muscles of the hand with the exception of the abductor, tlie 

 opponens, the outer head of the flexor brevis pollicis, and the two outer lumbri- 

 cales. 



(ft) The nerves to the flexor carpi ulnaris and to tlie inner two divisions of 

 the flexor profundus digitorum arise from the ulnar in the upper third of the 

 forearm. 



(6) The Palmar Cutaneous Branch, — About the middle of the forearm it gives 

 off two cutaneous Ijranches; one pierces the fascia and anastomoses with the anterior 

 branch of the internal cutaneous nerve, and the other, the palmar cutaneous branch, 

 runs downwards in front of the ulnar artery, and is conducted liy the vessel intct 

 the palm. It furnishes some filaments to the vessel, and ends in the integument 

 covering the central depressed surface of the })alm and supjtlies a few twigs to the 

 skin of the hypothenar eminence. 



(c) The dorsal or posterior cutaneous branch arises al)out two inches 

 above the Avrist-joint, and passes backwards under covi'r of tlie lh>xor carpi ulnaris 

 to reach the dorsal aspect of the wrist. It crosses superficial to the tendon of the 

 extensor carpi ulnaris innnediately below the lower end of the idna, and, after 

 giving off twigs to supply the skin of the dorsum of the hand, divides into three 

 l)ranches, namely: a branch to the inner l)order of the little finger; a branch which 

 divides to supply the contiguous borders of the ring and little fingers, and a branch 

 which communicates with the radial and participates in the supi)ly of the adjacent 

 borders of the ring an<l middle fingers. 



(d) The superficial terminal branch of the ulnar nerve gives off a branch to 



