BEACHIAL CUTANEOUS NERVES. 587 



Small internal cutaneous nerve. — The smaller internal cutaneous 

 nerve, or nerve of Wrisberg, destined for the supply of the integument 

 of the lower half of the upper arm on the inner and posterior aspect, 

 commonly arises from the inner cord of the brachial plexus in union 

 with the larger internal cutaneous and ulnar nerves. In the axilla it 

 lies close to the axillary vein, but it soon appears on the inner side of 

 that vessel, and communicates with the intercosto-humeral nerve. It 

 then descends along the inner side of the brachial vessels to about the 

 middle of the arm, where it pierces the fascia, and its filaments are 

 thence continued to the interval between the internal condyle of the 

 humerus and the olecranon. 



Brandies.— In the lower third of the arm, branches of this small nerve are 

 directed almost horizontally to the integument on the posterior aspect : and the 

 nerve ends at the elbow by dividing into several filaments, some of which are 

 diiected for^-ards over the inner condyle of the humerus, while others ai-e pro- 

 longed downwards behind the olecranon. 



Connection n-ith the uifcrn^sfo-lnimiral nerve. — This connection presents much 

 variety in different cases : — in some, there are two or more intercommunications, 

 forming a kind of plexus on the posterior boundary of the axillary space ; in 

 others, the intercosto-humeral nerve is of larger size than usual, and takes the 

 place of the nerve of Wrisberg, only receiving in the axilla a small filament from 

 the brachial i:)lcxus , and this small communicating filament represents in such 

 cases the nerve of "W'risberg. 



Musculo-cutaneous nerve. — The musculo-cutaneous or external 

 cutaneous nerve is deeply placed between the muscles as far as the 

 elbow, and below that point is immediately under the integument. 

 Arising from the brachial plexus opposite the small pectoral muscle, it 

 perforates the coraco-brachialis muscle, and, passing obliquely across 

 the arm between tlie biceps and brachialis anticus muscles, reaches the 

 outer side of the biceps a little above the elbow. Here it perforates the 

 fascia, and nearly opposite the elbow-joint it passes behind the median- 

 cephalic vein, and, inclining outwards, divides into two branches which 

 supply the integument on the outer side of the forearm, one on the 

 anterior, the other on the posterior aspect. 



A. Branches ix the arm : — 



a. A branch to the coraco-brachialis and short head of the biceps is given off 

 before the nerve pierces the former muscle ; and other filaments are furnished to 

 the coraco-brachialis, while the nerve lies among its fibres. 



b. Branches to the biceps and brachialis anticus are given off while the nerve 

 is between those muscles. 



c. Small filaments are given to the humerus and elbow-joint. 



B. Branches ix the forearm : — 



a. The anfer'wr branch descends near the radial border of the forearm. It is 

 placed in front of the radial artery near the wrist, and distributes some filaments 

 over the ball of the thumb. Piercing the fascia, it accompanies the artery to the 

 back part of the caquis. This part of the nerve is connected at the wrist with a, 

 branch of the radial nerve. 



b. The jwsterior branch is directed outwards to the back of the forearm, and 

 ramifies in the integument of the lower third, extending as far as the wrist. It 

 communicates with a branch of the radial nerve, and with the external cutaneous 

 branch of the musculo-spu-al nerve. 



Summary. — The musculo-cutaneous nerve supplies the coraco- 

 brachialis, biceps, and brachialis anticus muscles, and the integument 



