THE BRACHIAL PLEXUS. 1301 



It supplies the flexor longus pollicis, the radial half of the flexor profundus digitorum 

 and the pronator quadratus. It distributes filaments to the interosseous membrane, the anterior 

 interosseous vessels, the shafts of the radius and ulna (the twigs to these bones entering 

 them with the nutrient arteries) , the periosteum of the radius and ulna and the radio-carpal 

 articulation. 



d. The palmar cutaneous branch (r. cutaneus palmaris) (Fig. 1097) leaves the median 

 at a varying distance above the wrist. It becomes superficial near the upper margin of the 

 anterior annular ligament by piercing the deep fascia between the flexor carpi radialis and the 

 palmaris longus. It supplies the skin of the palm and inosculates with the palmar cutaneous 

 branch of the ulnar and with filaments of the radial and musculo-cutaneous nerves. 



e. The muscular branch in the hand (r. muscularis) (Fig. 1097) is a short nerve which 

 arises below the anterior annular ligament and curves outward toward the base of the thumb. 

 It breaks up into filaments which supply the abductor pollicis, the opponens pollicis and the 

 superficial head of the flexor brevis pollicis. 



f. The digital branches (Fig. 1097) are five in number and, with the exception of 

 the twigs supplying the two outer lumbricales, are purely sensory. They arise from the 

 median, a short distance below the anterior annular ligament of the wrist ( nn. digitales volares 

 communes) and pass distally beneath the superficial palmar arch and over the flexor tendons. 

 As they approach the interdigital clefts they pass between the primary divisions of the median 

 portion of the palmar fascia and become more superficial as they continue along the borders of 

 the fingers (nn. digitales volares proprii). 



The first lies along the radial side of the thumb and inosculates around its radial aspect 

 with the radial nerve. 



The second occupies the ulnar side of the thumb. 



The third gives off a branch to the first lumbricalis and supplies the radial side of the index 

 finger. 



The fourth supplies the second lumbricalis and then divides into two branches which are 

 distributed to the adjacent sides of the index and middle fingers. 



The fifth, after being connected with the ulnar nerve by a stout filament (r. anastomot- 

 icus cum n. ulnare), divides for the supply of the adjoining aspects of the middle and ring 

 fingers. 



In the fingers these nerves lie anterior to the vessels and in their course toward the tip 

 of the finger they give off anterior and posterior branches, the latter supplying the skin over the 

 middle and distal phalanges of the index, middle and ring fingers and over the distal phalanx of 

 the thumb. Twigs are supplied to the interphalangeal articulations and near the end of the finger 

 each of the five breaks up into two terminal branches, one of which is destined for the sensitive 

 skin over the anterior portion of the distal phalanx and the other for the matrix of the nail. 



Variations. Some of these are described on page 1298. The fibres usually contributed to 

 the median nerve by the first thoracic may be wanting. Either the outer or the inner head may 

 consist of two nerve-bundles. The point at which the heads unite is a very variable one and 

 has been found as far down as the elbow. The heads may enclose the axillary vein instead of 

 the artery. In those instances, many of which have been found in the anatomical rooms of the 

 University of Pennsylvania, in which a single large branch of the axillary artery gives off the 

 two circumflex arteries, the subscapular and the two profunda arteries, this trunk, instead of the 

 axillary artery, is embraced by the heads of the median nerve. The inner head, the outer head 

 or the median itself may pass behind the axillary artery instead of in front. The outer head has 

 been seen to arise in the middle of the arm and pass behind the artery to join the inner head. 

 One instance has been reported in which the median entered the forearm over the pronator radii 

 teres instead of between the heads of that muscle. It has been seen lying on the superficial 

 surface of the flexor sublimis digitorum. The median may be cleft for a short distance in the 

 forearm, giving passage to the ulnar artery or one of its branches, to the superficial long head 

 of the flexor longus pollicis or to an extra palmaris longus muscle. A communication in the 

 arm between the median and ulnar nerves has been noted in one instance. A similar connection 

 in the forearm, occurring in numerous ways, is found in from 20-25 per cent, of cases examined. 

 A connection with the ulnar in the hand may pass either from the ulnar to the median or from 

 the median to the ulnar. The anterior interosseous has been seen to receive a filament from 

 the musculo-spiral through the interosseous membrane, and inosculation between the two 

 interosseous nerves has been noted at the lower part of the forearm ; according to Rauber, 

 this is the normal arrangement. One case has been described in which the abductor indicis 

 was supplied by the median. During the exchange of position between the digital branches 

 of the median nerve and the digital arteries the former are often pierced by the latter. The 

 fifth digital branch may arise in the forearm and enter the hand independently. 



Practical Considerations. A pure paralysis of the median nerve is rare, and 

 is almost always traumatic in origin. The paralysis is more commonly a part of a 

 more extended involvement of the brachial plexus. When this nerve is paralyzed 

 above there is inability to pronate the forearm or flex the wrist properly, since the 



