MUSCULO-SPIRAL,- RADIAL XERVE. 



653 



in some instances extending as far as the olecranon. This nerve is accompanied by a 

 small cutaneous artery. 



.B. Posterior branches : 



These consist of a fasciculus of muscular branches which supply the outer head of the 

 triceps muscle and the anconeus. The branch of the anconeus is slender, and remark- 

 able for its length; it descends in the substance of the triceps to reach its destination. 



C. External branches : 



(a) The muscular branches supply the supinator longus, extensor carpi radialis 

 longior, (the extensor carpi radialis brevior receiving its nerve from the posterior 

 interosseous,) and occasionally give a small branch to the brachialis anticus. 



(6) The external cutaneous branches, two in number, arise where the nerve pierces 

 the external intermuscular septum. 



The upper branch, the smaller of the two, is directed downwards to the fore part 

 of the elbow, along the cephalic vein, and distributes filaments to the lower half of 

 the upper arm on the anterior aspect. The lower branch extends as far as the wrist, 

 distributing offsets to the lower half of the arm, and to the forearm, on their pos- 

 terior aspect, and is connected near the wrist with a branch of the external cutaneous 



Fig. 433. DORSAL CUTANEOUS NERVES 

 OP THE HAND. J 



The distribution delineated in this 

 figure is not the most common, there being 

 a larger than usual branch of the ulnar 

 nerve : 1, the radial nerve descending 

 beside the principal radial cutaneous vein ; 

 2, and 3, dorsal branches to the two sides 

 of the thumb ; 4, branch to the radial 

 side of the forefinger ; 5, branch to the 

 fore finger and middle finger, communi- 

 cating with one from the ulnar nerve; 



6, the posterior branch of the ulnar nerve ; 



7, communicating twig ; 8, collateral 

 branch to the middle and ring fingers ; 

 9, collateral branch to the ring and little 

 fingers ; 10, branch to the inner side of 

 the hand and little finger. 



RADIAL NERVE. 



The radial nerve, continuing 

 straight down from the musculo- 

 spiral, is concealed by the long 

 supinator muscle, and lies a little 

 to the outer side of the radial 

 artery. This position beneath the 

 supinator is retained to about three 

 inches from the lower end of the 

 radius, where the nerve turns back- 

 wards beneath the tendon of the 

 muscle, -and becomes subcutaneous. 

 It then separates into two branches, 

 which ramify in the integument on 



the dorsal aspect of the thumb and the next two fingers in the following 

 manner. 



