MEDIAN". 571 



and ulnar nerves. It passes through the axillary space, at first lying beneath, and 

 then on the inner side of, the axillary vein, and communicates with the intercosto- 

 humeral nerve. It then 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 

 elbo\v, where some filaments are lost in the integument in front of the inner con- 

 dyle, and others over the olecranon. It communicates with the inner 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 Wrisberg, receiving merely a filament of communication from the 

 brachial plexus, which represents this 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. 288) has received its name from the course it takes 

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

 and 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. 

 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 occa- 

 sionally 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, to within two 

 inches above the annular ligament, where it becomes more superficial, lying between 

 the Flexor sublimis and Flexor carpi radialis, covered by the integument and 

 fascia. It then passes beneath the annular ligament into the hand. 



Branches. No branches are given off from the median nerve in the arm. 

 In the forearm, its branches are the muscular, anterior interosseous, and palmar 

 cutaneous. 



The muscular branches supply all the superficial muscles on the front of the 

 forearm, except the Flexor carpi ulnaris. These branches are derived from the 

 nerve near the elbow. The branch furnished to the Pronator radii teres often 

 arises above the joint. 



The anterior interosseous supplies the deep muscles on the front of the fore- 

 arm. It accompanies the anterior interosseous artery along the interosseous 

 membrane, in the interval between the Flexor longus pollicis and Flexor pro- 

 fundus digitorum ruuscles, both of which it supplies, and terminates below in the 

 Pronator quadratus. 



The palmar cutaneous branch arises from the median nerve at the lower part 

 of the forearm. It pierces the fascia above the annular ligament, and divides 

 into two branches ; the outer one supplies the skin over the ball of the thumb, and 

 communicates with the external cutaneous nerve ; the inner one supplies the inte- 

 gument of the palm of the hand, anastomosing with the cutaneous branch of the 

 ulnar. Both nerves cross the annular ligament previous to their distribution. 



In the palm of the hand, the median nerve is covered by the integument and 

 palmar fascia, and rests upon the tendons of the Flexor muscles. In this situation 

 it becomes enlarged, somewhat flattened, of a reddish color, and divides into two 

 branches. Of these, the external one supplies a muscular branch to some of the 

 muscles of the thumb, and digital branches to the thumb and index-finger ; the 

 internal branch supplying digital branches to the middle finger and part of the 

 index and ring fingers. 



The branch to the muscles of the thumb is a short nerve, which subdivides to 

 supply the Abductor, Opponens, and outer head of the Flexor brevis pollicis 

 muscles ; the remaining muscles of this group being supplied by the ulnar nerve. 



