THE MEDIAN NERVE. 301 



usual, or even absent, in which case the deficiency is generally compensated by the radial 

 nerve (p. 306). in rare cases by the lower external cutaneous of the musculo-spiral (p. 304), or 

 by the internal cutaneous (p. 296). Its area of digital distribution is seldom increased, but it 

 was found by Hepburn supplying 1 all four finders in a case of absence of the radial nerve. 

 Its filaments often reach to the radial side of the second metacarpal bone, and in one instance 

 they were followed by Zander to the back of the first phalanx of the thumb. 



SUMMARY. The ulnar nerve gives cutaneous filaments to the lower part of the 

 forearm (to a small extent), and to the inner part of the hand on its palmar and 

 dorsal aspects. It supplies the following muscles, viz., the ulnar flexor of the carpus, 

 the deep flexor of the fingers (its inner half), the short muscles of the little finger 

 with the palmaris brevis, the interosseous muscles of the hand, the inner two 

 lumbricales, and the adductores pollicis. Lastly, it contributes to the nervous 

 supply of the joints of the elbow, wrist, and hand. 



Median nerve. The median nerve, composed of fibres proceeding from the 

 lower three cervical and the first dorsal nerves, arises by two roots or heads, one from 

 the outer, the other from the inner cord of the brachial plexus. Commencing by 

 the union of these roots in front or on the outer side of the axillary artery, the 

 nerve descends in contact with the brachial artery, lying on its antero-lateral aspect 

 as far as the middle of the arm, then gradually passes inwards over it, and near the 

 elbow gains the inner side of the vessel. Sinking into the hollow at the bend of the 

 elbow, the nerve passes beneath the superficial portion of the pronator teres, but over 

 the deep slip of that muscle, by which it is separated from the ulnar artery, and 

 continues straight down the front of the forearm between the flexor sublimis and 

 flexor profundus digitorum muscles. Arrived near the wrist it lies beneath the 

 fascia, between the tendons of the flexor sublimis and palmaris longus internally 

 and that of the flexor carpi radialis externally. It then enters the palm behind the 

 annular ligament, and rests on the flexor tendons. Somewhat enlarged, and of a 

 slightly reddish colour, it here separates into two parts of nearly equal size. One of 

 these (the external) supplies some of the short muscles of the thumb, and gives 

 digital branches to the thumb and the index finger ; the second portion supplies the 

 middle finger, and in part the index and ring fingers. 



The median nerve usually gives no branch in the upper arm. 



A. Branches in the forearm. 



(a) Articular Iranches. These are one or two filaments to the front of the 

 elbow-joint (Riidinger). 



(1) Muscular Iranches arise either together or separately in the neighbourhood 

 of the elbow and pass to the pronator teres (6 c\ flexor carpi radialis (6 c), palmaris 

 longus and the condylo-ulnar head of the flexor sublimis digitorum (7, 8 c, Id). A 

 separate offset enters the radial head of the flexor sublimis, and a third branch 

 supplying the index finger belly of the same muscle is given off by the trunk at a 

 lower level in the forearm. 



(c) Anterior interosseous nerve (7, 8 c, 1 d or 8 c, 1 d). This is the longest branch 

 of the median nerve, and it supplies the deeper muscles of the front of the forearm. 

 Leaving the main trunk a little below the elbow, it runs downwards with the artery 

 of the same name on the interosseous membrane to the deep surface of the pronator 

 quadratus muscle, in which it ends. It distributes branches to the flexor longus 

 pollicis and the outer half of the flexor profundus digitorum, between which it lies ; 

 a slender branch is given off to the interosseous membrane, along or in which it 

 descends, dividing into two, and supplying filaments to the membrane, to the 

 anterior interosseous vessels, to the shafts of the radius and ulna with the medullary 

 arteries, and to the periosteum ; and from the lower end of the nerve a twig is con- 

 tinued to the front of the wrist-joint. Small Pacinian bodies are found on the 

 branches passing to the bone and periosteum (Rauber). 



VOL, III., PT. 2. U 



