I 3 o6 HUMAN ANATOMY. 



Further description of the communications of the ulnar nerve, in addition to those just 

 mentioned, will be found in connection with the median nerve (page 1301). 



Variations. The ulnar may have a root from the seventh cervical nerve by way of the outer 

 cord, or may be derived from the eighth cervical only or from the seventh and eighth. It may 

 pass in front of the internal condyle or lie behind the condyle and slip forward during flexion of 

 the elbow. Connecting twigs have been seen passing from the ulnar to the internal cutaneous, 

 to the median in the upper arm and to the musculo-spiral. Frequently there is an associating 

 branch in the forearm between the median and the ulnar. Muscular twigs have been noted as 

 passing to the inner head of the triceps, the flexor sublimis digitorum, the first and second 

 fumbricales and the superficial head of the flexor brevis pollicis. Deficiencies in the branch to 

 the dorsum of the hand have been observed to be compensated for by the radial, the inferior 

 external cutaneous branch of the musculo-spiral or the internal cutaneous. In a specimen with 

 absence of the radial nerve all four fingers were supplied by the ulnar. The dorsal terminal 

 filaments of the ulnar tend to encroach on the radial side of the hand and in one case reached 

 the dorsum of the first phalanx of the thumb. 



Practical Considerations. In paralysis of the ulnar nerve, flexion of the wrist 

 is impaired, and also (on account of the flexor carpi ulnaris paralysis) lateral motion 

 toward the ulnar side (adduction). There is difficulty in spreading the fingers, as 

 all the interossei are supplied by this nerve. The hand will be ' ' clawed' ' from the 

 paralysis of the interossei, which now fail to resist the action of the extensors on 

 the proximal phalanges, and of the flexors on the distal and medial, except in the 

 middle and ring fingers where the flexor profundus its ulnar half being paralyzed 

 has only a slight influence on the distal phalanges. Besides the flexor carpi ulnaris, 

 the ulnar half of the flexor profundus and the interossei, the ulnar nerve supplies 

 all the hypothenar muscles, the adductor pollicis, the inner half of the flexor brevis 

 pollicis and the two ulnar lumbricales ; consequently the hypothenar eminence dis- 

 appears and the thenar eminence shows atrophy in ulnar paralysis. This nerve is 

 involved particularly in those whose occupations require them to press their elbows 

 against hard objects or to strike blows frequently with the ulnar border of the hand. 

 It may be injured in fractures of the elbow, particularly of the internal condyle. In 

 the forearm and wrist it is the nerve most frequently injured. It is found on the inner 

 side of the brachial artery in the upper half of the arm, but in the lower half it passes 

 posteriorly to the bony interval between the internal condyle and the olecranon, 

 where it is readily located by pressure, which causes a tingling sensation down the 

 forearm. The same sensation is often produced by blows on the elbow, the nerve 

 being compressed between the internal condyle and the olecranon. It is the structure 

 most frequently damaged in excisions of the elbow. In the lower two-thirds of the 

 forearm it lies to the radial side of the flexor carpi ulnaris muscle and to the ulnar 

 side of the ulnar artery. At the wrist it passes over the anterior annular ligament in 

 the same relation to the artery and to the radial side of the pisiform bone. 



14. THE SUBSCAPULAR NERVES. 



The subscapular nerves (nn. subscapulares) (Fig. 1092) arise from the posterior 

 cord and are usually three in number. Together they supply the three muscles which 

 form the posterior boundary of the axillary space. 



The upper or short subscapular nerve is composed of fibres which are 

 prolonged from the fifth and sixth cervical nerves. It often is either double in origin 

 or divides into two branches shortly after leaving the posterior cord. It arises 

 behind the circumflex nerve and after a short course enters the inner surface of the 

 subscapularis near the upper margin of that muscle. 



The middle or long subscapular nerve (n. thoracodorsalis), the largest of the 

 three, arises from the rear aspect of the posterior cord, behind the origin of the 

 musculo-spiral nerve. Its fibres are derived from the sixth, seventh and eighth 

 cervical nerves, the majority of them coming from the seventh. It takes a course 

 downward and outward on the posterior axillary wall behind the axillary artery, and 

 accompanies tin- suhscapular artery to the deep surface of the latissimus dorsi, before 

 entering which it breaks up into a number of strands. 



The lower subscapular nerve obtains its fibres from the fifth and sixth cer- 

 vical nerves. It arises from the posterior cord behind the origin of the circumflex 



