THE BRACHIAL PLEXUS 



1035 



the wrist, supplying the carpus. The nerve then passes downward to the ball of 

 the thumb, where it terminates in cutaneous filaments. It communicates with a 

 branch from the radial nerve 

 and with the palmar cuta- 

 neous branch of the median. 



The posterior branch passes 

 downward along the back 

 part of the radial side of the 

 forearm to the wrist. It sup- 

 plies the integument of the 

 lower third of the forearm, 

 communicating with the 

 radial nerve and the external 

 cutaneous branch of the mus- 

 culospiral. The cutaneous 

 areas supplied by the mus- 

 culocutaneous nerve are in- 

 dicated in Figs. 762 and 763. 



Variations. The musculocu- 

 taneous nerve presents frequent 

 irregularities. It may adhere for 

 some distance to the median and 

 then pass outward, beneath the 

 Biceps, instead of through the 

 Coracobrachialis. Frequently 

 some of the fibres of the median 

 run for some distance in the mus- 

 culocutaneous and then leave it to 

 join their proper trunk. Less 

 frequently the reverse is the case, 

 and the median sends a branch to 

 join the musculocutaneous. In- 

 stead of piercing the Coracobra- 

 chialis muscle the nerve may pass 

 under it or through the Biceps. 

 Occasionally it gives a filament to 

 the Pronator teres muscle, and it 

 has been seen to supply the back 

 of the thumb when the radial 

 nerve was absent. 



The Internal Cutaneous 

 Nerve (//.. cutaneus antebrachii 

 medialifs) (Figs. 759 and 764). 

 or medial cutaneous nerve of 

 the forearm, is one of the 

 smallest branches of the bra- 

 chial plexus. It arises from 

 the inner cord in common 

 with the ulnar nerve and 

 internal head of the median 

 nerve, and, at its commence- 

 ment, is placed on the inner 

 side of the axillary artery, 

 and afterward of the brachial artery. It derives its fibres from the eighth cervical 

 and first thoracic nerves. This nerve gives off, near the axilla, a cutaneous 

 filament, which pierces the fascia and supplies the integument covering the Biceps 



FIG. 763. Cutaneous nerves of the upper limb, posterior aspect. 

 (W. Keiller. in Gerrish's Text-book of Anatomy.) 



