THE BRACHIAL PLEXUS. Ill 



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

 of the axillary, and afterward of the brachial 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 with 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 

 fascia and supplies the integument covering the Biceps muscle nearly as far as 

 the elbow. This filament lies a little external to the common trunk, from which 

 it arises. 



The anterior branch, the larger of the two, passes usually in front of, but 

 occasionally behind, the median basilic vein. It then descends on the anterior 

 surface of the ulnar side of the forearm, distributing filaments to the integument 

 as far as the wrist, and communicating with a cutaneous branch of the ulnar 

 nerve. 



The posterior branch passes obliquely downward on the inner side of the 

 basilic vein, passes in front of, or over, the internal condyle of the humerus to the 

 back of the forearm, and descends on the posterior surface of its ulnar side as far 

 as the wrist, distributing filaments to the integument. It communicates, above 

 the elbow, with the lesser internal cutaneous, and above the wrist with the dorsal 

 cutaneous branch of the ulnar nerve (Swan). 



The Lesser Internal Cutaneous Nerve (nerve of Wrisberg} (Fig. 413) is distrib- 

 uted to the integument on the inner side of the arm. It is the smallest of the 

 branches of the brachial plexus, and, arising from the inner cord with the internal 

 cutaneous and ulnar nerves, receives its fibres from the first dorsal nerve. It 

 passes through the axillary space, at first lying behind, and then on the inner side 

 of, the axillary vein, and communicates with the intercosto-humeral nerve. It 

 descends along the inner side of the brachial artery to the middle of the arm, 

 where it pierces the deep fascia, and is distributed to the integument of the back 

 part of the lower third of the arm, extending as far as the elbow, where some 

 filaments are lost in the integument in front of the inner condyle, and others 

 over the olecranon. It communicates with the posterior branch of the internal 

 cutaneous nerve. 



In some cases the nerve of Wrisberg and intercosto-humeral are connected by 

 two or three filaments which form a plexus at the back part of the axilla. In 

 other cases the intercosto-humeral is of large size, and takes the place of the 

 nerve of Wrisberff, receiving merely a filament of communication from the brachial 



O 7 O v . 



plexus, which represents the latter nerve. In other cases this filament is wanting, 

 the place of the nerve of Wrisberg being supplied entirely from the intercosto- 

 humeral. 



The Median Nerve (Fig. 413) has received its name from the course it takes 

 along the middle of the arm and forearm to the hand, lying between the ulnar 

 and the musculo-spiral and radial nerves. It arises by two roots, one from the 

 outer, and one from the inner, cord of the brachial plexus ; these embrace the lower 

 part of the axillary artery, uniting either in front or on the outer side of that 

 vessel. It receives filaments from the sixth, seventh, and eighth cervical and the 

 first dorsal. As it descends through the arm, it lies at first on the outer side of 

 the brachial artery, crosses that vessel in the middle of its course, usually in 

 front, but occasionally behind it, and lies on its inner side to the bend of the 

 elbow, where it is placed beneath the bicipital fascia, and is separated from the 

 elbow-joint by the Brachialis anticus. In the forearm it passes between the two 

 heads of the Pronator radii teres, and descends beneath the Flexor sublimis, lying 

 on the Flexor profundus, to within two inches above the annular ligament, where 

 it becomes more superficial, lying between the tendons of the Flexor sublimis 

 and Flexor carpi radialis, beneath, and rather to the radial side of, the tendon of 

 the Palmaris longus, covered by the integument and fascia. It then passes 

 beneath the annular ligament into the hand. In its course through the forearm it 

 is accompanied by a branch of the anterior interosseous artery. 



