254 The Brachial Plexus 



the ball of the little finger and of the muscular web between the meta- 

 carpal bones of the thumb and index-finger (abductor indicis, adductor 

 pollicis, and deep part of flexor brevis pollicis). All the metacarpal 

 bones become extremely prominent on the back of the hand, on account 

 of atrophy of the interosseous muscles. The patient is unable to 

 wrinkle the skin on the inner side of the palm (palmaris brevis) to 

 form the 'cup of Diogenes' ; he cannot span (abductor minimi digiti); 

 and he is able to bring the thumb towards the middle line of the hand 

 only by the action of the flexor longus pollicis, the muscles of the first 

 interosseous space being useless. 



The two inner fingers are ' clawed] or, as it is also called, en griffe 

 the two inner lumbricals and the interossei cannot flex the first pha- 

 langes nor extend the second and third (273) ; so the common extensor 

 keeps the first phalanges extended whilst the second phalanges are 

 kept slightly bent by the flexor sublimis. When this deformity is 

 extreme the metacarpo-phalangeal knuckles become hollowed, for the 

 extensor tendon is drawing back the first phalanx, and the interossei 

 and lumbricals are powerless to hinder it. 



The median is formed by two trunks, one from the inner, the other 

 from the outer cord fifth, sixth, seventh, eighth, and first the two trunks 

 join over the front of the third part of the axillary arteiy. The nerve then 

 lies to the outer side of the axillary and the beginning of the brachial 

 artery, and, crossing the latter in the middle of its course, is found, near 

 the elbow, on its inner side, resting upon the brachialis anticus. 



It enters the fore-arm between the two heads of the pronator radii 

 teres, and, crossing the ulnar artery, descends between the'superficial 

 and deep flexors of the fingers. Above the wrist, where the muscles 

 are ending in tendons, the nerve is exactly in the middle line between 

 the flexor carpi radialis and the outermost tendon of the flexor sub- 

 limis, under cover, but slightly to the inner side of the palmaris longus. 

 It then passes beneath the annular ligament, and widens out prepara- 

 tory to dividing into digital branches. 



In its course it supplies the pronator radii teres, flexor carpi radialis, 

 palmaris longus, and flexor sublimis digitorum. It gives off the an- 

 terior interosseous branch, which courses deeply, upon the membrane 

 supplying the flexor longus pollicis, the outer part of the flexor profun- 



dus, and the pronator quadratus. 

 A palmar cutaneous branch also 

 comes from the median ; it pierces 

 the deep fascia, and descends over 

 the annular ligament, 

 i, Palmar branch ; 2, its filaments to pulp ; j n the palm the median nerve 



3, its ungual twigs ; 4 and 5, distribution . a , , 



on dorsal aspect/ 1S flattened ; it rests on the tendons 



of the superficial flexor, under the 



protection of the palmar fascia, and gives branches for the three and 

 a-half outer digits, which, with the exception of those for the thumb, 



