THE FOREARM. 319 



between the superficial and deep layers of muscles. It lies on the flexor profundus 

 digitorum and is covered by the flexor sublimis ; about 5 cm. above the annular liga- 

 ment it becomes more superficial and lies in the interval between the palmaris longus 

 and flexor carpi radialis tendons and touching them. It then passes under the annu- 

 lar ligament to enter the palm of the hand. A branch of the anterior interosseous 

 artery called the comes nervi mediani accompanies the nerve in the forearm. 



Branches. The median nerve gives off muscular, volar (anterior) interosseous, 

 and palmar cutaneous branches, besides those in the hand. 



The superficial flexor muscles, with the exception of the flexor carpi ulnaris, 

 are supplied by branches directly from the main trunk near the elbow ; the one 

 to the pronator radii teres usually comes off above the elbow. The deep flexor 

 muscles, with the exception of the inner half of the flexor profundus digitorum, are 

 supplied by the volar (^anterior) interosseous branch. 



The volar (anterior) interosseous nerve leaves the main trunk of the median 

 just below the elbow and accompanies the volar (anterior) interosseous artery, 

 lying on the interosseous membrane between the flexor longus pollicis and the 

 flexor profundus digitorum. It supplies the flexor longus pollicis and radial half 

 of the flexor profundus muscles as well as the pronator quadratus. 



The palmar cutaneous branch is given off just above the annular ligament and 

 comes to the surface between the palmaris longus and flexor carpi radialis tendons. 

 It passes over the annular ligament to be distributed to the thenar eminence and 

 palm of the hand. 



Wounds of the Median Nerve. The median nerve may be wounded in 

 any part of its course in the forearm, but it is superficial only in its lower portion for 

 about 5 cm. above the wrist. From this point up it is covered by the flexor sublimis, 

 the flexor carpi radialis and the pronator radii teres. 



While these muscles tend to protect it from injury, if the traumatism is exten- 

 sive enough to divide it they render it all the more difficult to treat. Accompanying 

 the nerve, especially in the middle third of the forearm, is the comes nervi mediani 

 artery, which may cause annoying bleeding. Careless attempts to secure the artery 

 may injure the nerve. Should the nerve be divided, paralysis ensues of all the 

 superficial flexor muscles except the flexor carpi ulnaris, and of the deep muscles, 

 except the inner half of the flexor profundus. This includes the pronator radii teres 

 and pronator quadratus, so that the power of pronating the forearm is impaired 

 as well as the ability to flex the hand. The flexor carpi ulnaris and outer half (that 

 going to the ring and little fingers) of the flexor profundus digitorum are the only 

 flexor muscles not paralyzed. 



The paralyzed flexor muscles atrophy and the size of the forearm is much 

 reduced. There will also be impairment of the functions of sensation and motion in 

 the hand, which will be alluded to later. 



Operations. To find the nerve in the upper third of the forearm an incision 

 may be made at the inner side of the biceps tendon and brachial artery. The 

 median nerve will be found to the inner side of the artery and may be followed 

 down. When the pronator radii teres is reached it must either be drawn to the 

 ulnar side or divided. 



The fascial expansion covering the flexor sublimis is next reached; it must be 

 slit up and the muscular fibres parted to reach the nerve lying between it and the 

 flexor profundus, with the volar (anterior) interosseous nerve alongside. 



To reach the nerve in the middle third of the forearm the guide should be the 

 palmaris longus tendon. The nerve lies in a line joining the outer edge of the palma- 

 ris longus tendon at the wrist and the brachial artery at the inner side of the biceps 

 tendon at the elbow. If an incision is made in the middle of the forearm one comes 

 down on the belly of the flexor carpi radialis muscle and it is necessary to part its 

 fibres as well as those of the flexor sublimis beneath. If one goes a little lower down 

 and places the incision between the palmaris longus and flexor carpi radialis the latter 

 may be drawn outward, but the fascia covering the flexor sublimis will still have to 

 be incised. The comes nervi mediani artery will be found accompanying the nerve. 



To reach the nerve in its lower third is the easiest because it becomes super- 

 ficial about 5 centimetres (2 in.J above the wrist. Here it lies either beneath the 



