72 THE SUPERIOR EXTREMITY 



nerve leaves the artery to gain the dorsum of the wrist by 

 passing under cover of the brachio-radialis. Here it is joined 

 by communicating twigs from the dorsal branch of the musculo- 

 cutaneous and from the dorsal cutaneous nerve of the forearm 

 (lower external cutaneous branch of the musculo-spiral nerve). 

 It is a purely sensory nerve and terminates on the back of the 

 hand by supplying the skin on the dorsal aspects of the thumb, 

 index, and middle fingers, and the radial side of the ring finger. 

 Injuries to this nerve are discussed on p. 102. 



The dorsal digital nerves do not reach the tips of the fingers 

 but end over the second phalanges ; the remainder of the dorsal 

 surface is supplied by the digital nerves of the palm. 



Radial Artery. The course of the radial artery may be 

 indicated by a line drawn from the termination of the brachial 

 artery (p. 42) to the navicular tubercle. In the proximal 

 two-thirds of its course it will be found under cover of the 

 brachio-radialis. In the proximal third it lies on the supinator, 

 and the superficial (radial) branch of the radial (musculo-spiral) 

 nerve approaches it from the lateral side. In the middle third it 

 lies on the pronator teres and the radial head of the flexor 

 digitorum sublimis while the nerve is close to its lateral side. 

 The distal third of the artery is subcutaneous and lies upon the 

 flexor pollicis longus and the radius (Fig. 25). 



It gives off the radial recurrent (p. 43) near its origin, and 

 the superficial volar in the distal part of the forearm. The 

 latter runs through or over the short muscles of the thumb to 

 join the ulnar artery and complete the superficial palmar arch 



(Fig. 30). 



If the radial or ulnar artery is severed in more than one 

 place, all the cut ends must be tied, as the muscular branches 

 of the radial, ulnar, and volar (anterior) interosseous arteries 

 anastomose very freely throughout the forearm. When the 

 radial artery is wounded at the wrist, both ends must be ligatured, 

 owing to the free anastomosis in the hand (p. 86). 



The Median Nerve, which enters the forearm between the 

 superficial and deep heads of the pronator teres (p. 68), can 

 be indicated by a line, drawn from a point midway between 

 the medial epicondyle and the biceps tendon to a point at the 

 wrist, slightly to the medial side of the tendon of the flexor 

 carpi radialis. It lies between the superficial and deep groups 

 of muscles, and is bound down to the deep surface of the flexor 

 digitorum sublimis. It supplies the superficial group (p. 69), 



