646 THE BRACHIAL PLEXUS. 



major muscle above the long head of the triceps, and separates into an 

 upper and a lower branch, which are distributed to the deltoid and teres 

 minor muscles, the integument of the shoulder, and the shoulder-joint. 



a. The upper portion winds round the upper part of the humerus, extending to the 

 anterior border of the deltoid muscle, to which it is distributed. One or two 

 cutaneous filaments, penetrating between the muscular fibres, are bent downwards 

 and supply the integument over the lower part of the muscle. 



b. The lower branch supplies offsets to the back part of the deltoid, and furnishes 

 the nerve to the teres minor, which is remarkable in presenting a gangliform enlarge- 

 ment. It then turns round the posterior border of the deltoid below the middle, and 

 ramifies in the integument over the lower two-thirds of that muscle, one branch 

 extending to the integument over the long end of the triceps muscle. 



c. An articular filament for the shoulder-joint arises near the commencement of 

 the nerve, and enters the capsular ligament below the subscapular muscle. 



INTERNAL CUTANEOUS NERVE. 



At its origin from the inner cord of the brachial plexus, this nerve is 

 placed on the inner side of the axillary artery. It becomes cutaneous about 

 the middle of the arm, and after perforating the fascia, or, in some cases, 

 before doing so, is divided into two parts ; one destined for the anterior, 

 the other for the posterior surface of the forearm. 



a. The anterior branch crosses at the bend of the elbow behind (in some cases 

 over) the median basilic vein, and distributes filaments in front of the forearm, as 

 far as the wrist; one of these is, in some instances, joined with a cutaneous branch 

 of the ulnar nerve. 



b. The posterior branch inclines obliquely downwards at the inner side of the basilic 

 vein, and winding to the back of the forearm, over the prominence of the internal 

 condyle of the humerus, extends somewhat below the middle of the forearm. Above 

 the elbow this branch is connected with the smaller internal cutaneous nerve (nerve 

 of Wrisberg), and afterwards communicates with the outer portion of the internal 

 cutaneous, and, according to Swan, with the dorsal branch of the ulnar nerve. 



c. A branch to the integument of the arm pierces the fascia near the axilla, and 

 reaches to, or nearly to the elbow, distributing filaments outwards over the biceps 

 muscle. This branch is often connected with the intercosto -humeral nerve. 



SMALL INTERNAL CUTANEOUS NERVE. 



The smaller internal cutaneous nerve, or nerve of Wrisberg, destined for 

 the supply of the integument of the lower balf 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 uluar 

 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. 



Branches. 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 directed forwards 

 over the inner condole of the humerus, while others are prolonged downwards 

 behind the olecranon. 



Connection with the intercosto-humeral nerve. This connection presents much 

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

 ing a kind of plexus on the posterior boundary of the axillary space ; in others, the 



