THE BRACHIAL PLEXUS. 839 



the subscapular artery, along the posterior wall of the axilla to the Latissimus 

 dorsi, through which it mav be traced as far as its lower border. 



The Circumflex Nerve (Fig. 501) supplies some of the muscles and the integu- 

 ment of the shoulder and the shoulder-joint. It arises from the posterior cord of 

 the brachial plexus, in common with the musculo-spiral nerve, and its fibres may 

 be traced through the posterior cord to the fifth, sixth, seventh, and eighth cer- 

 vical nerves. It is at first placed behind the axillary artery, between it and the 

 Subscapularis muscle, and passes downward and outward to the lower border of 

 that muscle. It then winds backward in company with the posterior circumflex 

 artery, through a quadrilateral space bounded above by the Teres minor, below 

 by the Teres major, internally by the long head of the Triceps, and externally by 

 the neck of the humerus, and divides into t\vo branches. 



The upper branch winds round the surgical neck of the humerus, beneath tb-e 

 Deltoid, with the posterior circumflex vessels, as far as the anterior border of that 

 muscle, supplying it, and giving off cutaneous branches, which pierce the muscle 

 and ramify in the integument covering its lower part. 



The loiver branch, at its origin, distributes filaments to the Teres minor and 

 back part of the Deltoid muscles. Upon the filament to the former muscle a 

 gangliform enlargement usually exists. The nerve then pierces the deep fascia, 

 and supplies the integument over the lower two-thirds of the posterior surface of 

 the Deltoid, as well as that covering the long head of the Triceps. 



The circumflex nerve, before its division, gives off an articular filament, which 

 enters the shoulder-joint below the Subscapularis. 



The Musculo-cutaneous Nerve (Fig. 500) (external cutaneous or perforans Cas- 

 serii) supplies some of the muscles of the arm and the integument of the fore- 

 arm. It arises from the outer cord of the brachial plexus, opposite the lower border 

 of the Pectoralis minor, receiving filaments from the fifth, sixth, and seventh 

 cervical nerves. It perforates the Coraco-brachialis muscle, passes obliquely between 

 the Biceps and Brachialis anticus to the outer side of the arm, and, a little above 

 the elbow, winds round the outer border of the tendon of the Biceps, and, perfo- 

 rating the deep fascia, becomes cutaneous. This nerve in its course through the 

 arm supplies the Coraco-brachialis (this branch often arises separately from the 

 outer cord). Biceps, and part of the Brachialis anticus muscles. It sends a small 

 branch to the bone, which enters the nutrient foramen with the accompanying 

 artery and a filament, from the branch supplying the Brachialis anticus, to the 

 elbow-joint. 



The cutaneous portion of the nerve passes behind the median cephalic vein, and 

 divides, opposite the elbow-joint, into an anterior and a posterior branch. 



The anterior branch descends along the radial border of the forearm to the 

 wrist, and supplies the integument over the outer half of the anterior surface. At 

 the wrist-joint it is placed in front of the radial artery, and some filaments, 

 piercing the deep fascia, accompany that vessel to the back of 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 the palmar cutaneous branch of the median. 



The posterior branch passes downward along the back part of the radial side 

 of the forearm to the wrist. It supplies the integument of the lower third of the 

 forearm, communicating with the radial nerve and the lower external cutaneous 

 branch of the musculo-spiral. 



The Internal Cutaneous Nerve (Fig. 500) is one of the smallest branches of the 

 brachial plexus. It arises from the inner cord in common with the ulnar and 

 internal head of the median, and at its commencement is placed on the inner 

 side of the axillary artery. It derives its fibres from the eighth cervical and first 

 dorsal nerves. It passes down the inner side of the arm, pierces the deep fascia 

 Avith the basilic vein, about the middle of the limb, and, becoming cutaneous, 

 divides into two branches, anterior and posterior. 



This nerve gives off, near the axilla, a cutaneous filament, which pierces the 



