654 



NERVES OF THE TIPPER LIMB. 



(a) The external branch extends to the radial side of the thumb, and is joined by an 

 offset of the external cutaneous nerve. It distributes filaments over the ball of the 

 thumb. 



(b) The internal portion communicates with a branch of the external cutaneous 

 nerve on the back of the forearm, and divides into digital branches ; one running 

 along the ulnar side of the thumb, a second on the radial side of the index finger, a 

 third dividing to supply the adjacent sides of the index and middle fingers, while a 

 fourth joins with an offset from the dorsal branch of the ulnar, and along with it 

 forms a branch for the supply of the contiguous sides of the middle and ring 

 fingers. These branches communicate on the sides of the fingers with the palmar 

 digital nerves. 



Sometimes the interspace between the middle and ring fingers is entirely supplied 

 by the radial, and at other times entirely by the ulnar nerve. 



POSTERIOR INTEROSSEOUS NERVE. 



This nerve, the larger of the two divisions of the musculo-spiral nerve, 

 winds to the back of the forearm through the fibres of the supinator brevis 



Fig. 434. 



Fig. 434. VIEW OP THE RADIAL SIDE OP THE FORE-ARM, 



SHOWING THE FINAL DISTRIBUTION OF THE MuSCULO- 



SPIRAL NERVE (from Hirschfeld and Leveille). 5 



The supinator longus, andextensores carpi radiales longior 

 and brevior have been divided, and their upper parts re- 

 moved ; the extensor communis digitorurn is pulled back- 

 wards by a hook, and the supinator brevis has been par- 

 tially dissected to show the posterior interosseous nerve 

 passing through it. 



1, placed upon the tendon of the biceps muscle, points 

 to the musculo-cutaneous nerve ; 1', near the wrist, the 

 lower part of this nerve and its plexus of union with the 

 radial nerve ; 2, trunk of the musculo-spiral nerve emerg- 

 ing from between the brachialis anticus, on which the 

 number is placed, and the supinator longus muscle ; 2', 

 its muscular twigs to the long supinator and long radial 

 extensor of the carpus ; 2", the posterior interosseous nerve 

 passing through the substance of the supinator brevis : 3, 

 placed upon the cut lower portion of the supinator longus, 

 the radial nerve ; 4, the external collateral nerve of the 

 thumb ; 5, the common collateral of the fore-finger and 

 thumb ; 6, the common collateral of the fore-finger and 

 middle finger ; 7, the twig of union with the dorsal branch 

 of the ulnar nerve ; 8, placed upon the common extensor 

 of the fingers, the muscular branches of the posterior inter- 

 osseous nerve to the long extensor muscles ; 9, upon the 

 extensor secundi internodii pollicis, the branches to the 

 short extensor muscles. 



muscle, and is prolonged between the deep and 

 superficial layers of the extensor muscles to the 

 interosseous membrane, which it approaches about 

 the middle of the forearm. 



Much diminished in size by the separation of 

 numerous branches for the muscles, the nerve lies 

 at the lower part of the forearm beneath the 

 extensor of the last phalanx of the thumb and 

 the tendons of the common extensor of the 

 fingers, and terminates on the back of the 



carpus in a gangliform enlargement, from which filaments are given to the 



adjoining ligaments and articulations. 



