224 MUSCLES OF THE UPPER LIMB. 



tentlons insertcJ partly into tlic ha?e of the first plialanx at the side, and 

 ])artly into the extensor tendon. The first jiahnar interosseous muscle 

 i)clong-s to the ulnar side of the index-finger : the others are placed on 

 the radial sides of the ring and little fingers. 



Varieties in the short muEcles of tlie hand. — The palmaria brevis varies 

 greatly in the strengtli of its mu.scular fibres, and somewhat also in their length 

 and chrection. It is sometimes entirely absent (in the proportion of one in forty- 

 five out of six hundred dissections by Macalister). It Ls also sometimes found 

 nmning into the flexor minimi digiti. 



The abductor poUicis (breves) muscle is frequently found divided into an outer 

 and an inner pait, — a condition described by Soemmerring as nonnal ; and 

 accessory slips have been observed connected with it, — in some instances pro- 

 ceedmg from the styloid process (CruveiUiier and Turner), and in others from 

 the opponens poUicis (Slacalister). 



The flexor brevis poUicis is a variable muscle, especially in its deeper belly, a, 

 part of which shows a tendency to run more or less in connection %\T[th the 

 adductor poUicis ; and in the same manner the latter muscle is subject to varia- 

 tion in its breadth of origin and extent in inverse proportion to those of the 

 flexor brevis (Dui-sy in Henle and Pfeifer's Zeitsch. 1853). 



The abductor minimi digiti is found in some cases partially divided into two 

 or even into three slips, and in others to be united with the flexor brevis. 



Tlie opponentes muscles are subject to varieties chiefly affecting their extent, 

 and the degree of their union with or separation from the neighbouring muscles. 



The interossei muscles present some variations but not of any great mag-nitude. 

 They are occasionally double in one or more of the spaces, and sometimes, 

 though rarely, a i^almar mterosseous has been observed in the first space (Hoale 

 and Wood). The an-angement which usually exists in the foot, and which is 

 peculiar to man, has also been observed to occur in the hand. 



Nerves of the muscles of the hand. — The median nerve supplies branches 

 to the abductor poUicis, the flexor brevis and opponens immediately below the 

 anniUar ligament, and to the two first lumbricalcs muscles from the first and 

 second digital collateral nerves respectively. The iilnar nerve, besides giving a 

 twig to the palmaris brevis, furnishes by its deep palmar division branches to 

 the two internal lumbricales, all the interossei, the adductor, and the deep head 

 of the flexor brevis poUicis muscles. 



ACTIONS OP THE MUSCLES OF THE FOKEARM AND HAND. 



Tlie muscles of the foreann may be distinguished according to theii* actions as 

 pronators and supinators, flexors and extensors of the wrist, and long flexors and 

 extensors of the fingers ; those of the hand are flexors and extensors, adductors, 

 abductors and opposers of the fingers ; the terms adduction and abduction being 

 here used with reference to the middle of the hand. 



Pronation is mainly effected by the pronator teres and pronator quadratus : the 

 flexor carjii radialis also contributes sliglitly to this movement. The i^ronator 

 teres is fitted to flex the elbow when pronation has been completed, or when it 

 is prevented by antagonistic muscles. 



Siq)iniition is eft'ected princijially by the supinator brevis, the supinator 

 longus only i^artially accomplishing this action. The latter muscle is princii:>aUy 

 a ftcxo)' of the elbow, acting, however, only after that movement has been 

 begun by other muscles. By the successive and alternating action, however, of 

 the pronators and supinators and of the flexors and extensors of the caiijus, a 

 more complete rotation of the hand is produced, so that the ulna as well as the 

 radius moves round a fixed axis which is nearly in the line of the middle finger, 

 as may be well seen In the use of a corkscrew or other like movements. When 

 stiU more extensive movements of this kind are effected, they are accompanied 

 by rotation of the whole limb at the shoiUder- joint. 



Flexion of the n-rht is produced by the radial and ulnar flexors of the cai-pus, 

 and is aided by the flexors of the fingers when the action of those muscles on 



