THE BRACHIAL PLEXUS 363 



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supplies dorsally the little and inner half of the ring finger. 

 The latter communicates with the contiguous branch of the 

 radial. 



3. In the palm are the superficial and deep branches. The 

 former supplies the skin and palmaris brevis and digital branches 

 to the little and inner half of the ring fingers, the latter join- 

 ing a branch of the median. The latter, passing between flexor 

 brevis and abductor minimi digiti, supplies all the muscles 

 of the hand except those supplied by the median nerve, and 

 sends filaments to the wrist-joint. 



The musculospiral nerve is from the posterior cord and runs 

 behind the axillary and brachial vessels, and, later, in the 

 musculospiral groove with the superior profunda artery, pierces 

 the external intermuscular septum to the anterior aspect of 

 the arm, then between the brachialis anticus and supinator 

 longus. In front of the outer condyle it divides into the radial 

 and posterior interosseous nerves. 



BRANCHES. Muscular and cutaneous. 



Muscular Branches. These leave the nerve, as their names 

 imply, at the inner, posterior, and outer parts of the arm. 

 The internal supplies the inner and middle heads of the triceps; 

 the posterior supplies the outer head of the triceps and the 

 anconeus; the external supplies the supinator longus, extensor 

 carpi radialis longior, and the brachialis anticus. 



Cutaneous Branches. The internal arises before the nerve 

 enters the musculospiral groove, supplies the inner side of the 

 posterior aspect of the arm; the two external pierce the outer 

 head of the triceps close to its origin. The upper supplies the 

 lower part of the upper arm; the lower, the lower half of the 

 arm, forearm, and wrist dorsally, joining the posterior branch 

 of the musculocutaneous. 



The radial nerve is a purely sensory nerve, it is overlapped 

 by and runs parallel with the supinator longus, finally runs 

 backward beneath its tendon, just above the wrist, pierces 

 the fascia, and divides into two branches. Of these, the external 

 supplies the radial side and ball of the thumb, and joins a 

 branch of the musculocutaneous; the internal, after communi- 

 cating with the musculocutaneous, supplies dorsally digital 

 branches to the thumb and index, index and middle, middle 

 and outer half of the ring fingers. 



This last joins with the contiguous branch of the dorsal 



