302 THE SPINAL NERVES. 



(d) The palmar cutaneous branch arises a variable distance above the wrist, and 

 pierces the fascia of the forearm between the tendons of the flexor carpi radialis and 

 palmaris longus, close to the annular ligament, to terminate in the integument of 

 the palm, where it communicates with the palmar cutaneous branch of the ulnar 

 nerve. Some filaments are distributed over the thenar eminence, and form com- 

 munications with twigs of the radial or external cutaneous nerve. 



B. Branches in the hand. 



(a) Branch to muscles of the thumb. This short nerve (6 c), arching outwards 

 immediately below the annular ligament, subdivides into branches for the abductor, 

 the opponens, and the outer head of the flexor brevis pollicis muscles. 



(#) Digital nerves. These are five in number, and belong to the thumb, and the 

 fingers as far as the outer side of the ring-finger. They lie at first beneath the 

 superficial palmar arch and its digital branches, but as they approach the clefts between 

 the fingers, they are close to the integument in the intervals between the longi- 

 tudinal divisions of the palmar fascia, and on the fingers the nerves lie in front of 

 the vessels. 



The first and second nerves lie along the sides of the thumb ; and the former (the 

 outer one) is connected with the radial nerve over the border of the thumb. 



The third, destined for the radial side of the index finger, gives a branch to the 

 first or most external lumbricalis muscle. 



The fourth supplies the second lumbricalis, and divides into collateral branches 

 for the adjacent sides of the index and middle fingers. 



The fifth, the most internal of the digital nerves, is connected by a cross branch 

 with the ulnar nerve, and divides to supply the adjacent sides of the ring and 

 middle fingers. It often gives a branch to the third lumbricalis, which then has a 

 double supply. 



Each digital nerve divides at the end of the finger into two branches, one of 

 which supplies the ball on the fore part of the finger, while the other ramifies in the 

 pulp beneath the nail. Branches pass from each nerve forwards and backwards to 

 the integument of the finger ; those passing backwards join the dorsal collateral 

 nerve, and supply mainly the integument over the second and third phalanges of the 

 middle three digits. Filaments are also furnished to the articulations of the fingers. 

 The volar digital branches of the median and ulnar nerves are beset with numerous 

 Pacinian corpuscles both in the palm and on the fingers : the number of these 

 bodies varies from 60 to 100 in each digit. 



Varieties. Occasionally the median nerve does not receive any fibres from the first 

 dorsal nerve. 



Either of the heads of the nerve may be double. The level at which the two heads join is 

 very variable : they have been found separate to the middle of the arm, and in one case 

 nearly as far as the elbow (Testut). Calori saw the two heads embracing the axillary vein as 

 well as the artery. The inner head may cross behind, instead of in front of, the axillary 

 artery. The whole nerve is often found passing- behind the brachial artery (Vol. II. p. 441). 

 The outer head has been seen by Turner passing behind the axillary artery, so that the trunk 

 of the nerve lay altogether to the inner side of the brachial artery ; and in another case 

 recorded by the same anatomist the outer head separated from the musculo-cutaneous in the 

 middle of the arm and crossed behind the brachial artery to join the inner head. Gruber and 

 Walsh have described cases in which the nerve entered the forearm over the pronator teres 

 muscle. It has also been seen running down the forearm superficial to the flexor sublimis 

 digitorum (G. D. T.). The nerve has been found split for a certain distance in the forearm, 

 the cleft giving passage to the ulnar artery (Testut) or a branch of that vessel (Mauclaire). or 

 to the superficial long head of the flexor longus pollicis (Davies-Colley, Taylor and Dalton, 

 J. W. Williams), or to a supernumerary long palmar muscle (Reid and Taylor). 



The frequent communication between the median and musculo-cutaneous nerves in the 

 arm has already been referred to (p. 299). One instance is recorded of a connection between 

 the median and ulnar nerves in the arm (p. 300). A communication between these nerves in 

 the upper part of the forearm is present in the proportion of one in four or five limbs, usually 



