926 THE NERVOUS SYSTEM 



In the upper part of the forearm it lies on the flexor digitorum profundus, covered 

 by the flexor carpi ulnaris. Near the junction of the upper and middle thirds of the 

 forearm it is joined by the ulnar artery, which accompanies it to its termination, 

 lying throughout on its radial side (fig. 683). In the lower part of the forearm it 

 still rests on the flexor digitorum profundus, but between the flexor carpi ulnaris and 

 flexor digitorum sublimis, and is covered only by skin and fascia. At a variable 

 point in this part of the forearm, usually about 5 to 8 cm. (2 to 3 in.) from the carpus, 

 the nerve divides into its two terminal branches, a dorsal branch to the dorsal aspect 

 of the hand, and a volar branch to the volar aspect. 



Branches. The ulnar resembles the median nerve in not furnishing any branches 

 to the upper arm. As it passes between the olecranon process and the internal 

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

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

 flexor digitorum profundus, and in the lower half it gives off the three cutaneous 

 branches. In the palm of the hand it supplies the integument of the hypothenar 

 eminence, the fifth digit, and half of the fourth digit, and part of the skin of the 

 dorsum. It also supplies the short intrinsic muscles of the hand with the exception 

 of the abductor pollicis, the opponens, the outer head of the flexor pollicis brevis, 

 and the two outer lumbricales. 



The nerves to the flexor carpi ulnaris and to the inner two divisions of the 

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

 forearm. 



Cutaneous Branches. About the middle of the forearm the ulnar nerve gives 

 off two cutaneous branches: one pierces the fascia and anastomoses with the volar 

 branch of the medial antibrachial (internal) cutaneous nerve, and the other, the 

 palmar cutaneous branch, runs downwards in front of the ulnar artery (fig. 683), 

 and is conducted by the vessel into the palm (fig. 680). It furnishes some filaments 

 to the vessel, supplies a few twigs to the skin of the hypothenar eminence, and ends 

 in the integument covering the central depressed surface of the palm. 



The dorsal or posterior cutaneous branch, usually the smaller of the terminal 

 branches, arises about 5 cm. (2 in.) above the wrist-joint, and passes backwards 

 under cover of the flexor carpi ulnaris to reach the dorsal aspect of the wrist (fig. 684) , 

 where it gives off delicate branches to anastomose with branches of the medial 

 antibrachial (internal) cutaneous, the dorsal antibrachial (external) cutaneous 

 branch of the radial (musculo-spiral) , the lateral antibrachial cutaneous of the mus- 

 culo-cutaneous nerve, and with branches of the superficial radial, and then divides 

 into five branches, the dorsal digitals (fig. 681), which are distributed to the ulnar 

 sides of the third, fourth, and fifth digits and the radial sides of the fourth and fifth 

 digits. These branches usually extend on the fifth digit only as far as the base of 

 the terminal phalanx, and on the fourth digit as far as the base of the second phalanx. 

 The more distal parts of these digits are supplied by palmar digital branches of the 

 ulnar nerve. 



The volar branch, the other terminal branch of the ulnar nerve, continues its 

 course between the flexor carpi ulnaris and flexor digitorum sublimis, on the inner 

 side of the ulnar artery, to the wrist, where, on the outer side of the pisiform bone, 

 it divides into a superficial and a deep branch (figs. 683 and 684). The latter 

 accompanies the deep branch of the ulnar artery into the interval between the abductor 

 digiti quinti and flexor digiti quinti brevis, and then passes through the fibres of the 

 opponens digiti quinti to reach the deep surface of the flexor tendons and their 

 synovial sheaths. It supplies the abductor and opponens digiti quinti, the flexor 

 digiti quinti brevis, the third and fourth lumbricales, all the interossei, the adductors 

 of the thumb, and the inner head, and occasionally the outer head, of the flexor 

 pollicis brevis. The superficial branch gives off a branch to supply the palmaris 

 brevis muscle, an anastomosing branch to the median nerve, and then divides into 

 two branches, the proper volar digital branch, which is distributed to the inner 

 side of the fifth digit on its volar aspect, and the common volar digital branch, 

 which passes underneath the palmar aponeurosis and divides into two branches, 

 which supply the contiguous margins of the fourth and fifth digits. These branches 

 usually supply also the dorsal surface of the second and third phalanges of the same 

 digits. 



The Median Nerve contains fibres of the sixth, seventh, and eighth cervical 

 nerves and of the first thoracic, and sometimes of the fifth cervical nerve. The 



