HAND 



faculty of opposing the thumb to the other lingers, 

 no an to H< i/e UJXHI the most minute objects a 

 faculty which i> carried to its highest degree of 

 perfection in man, in whom the whole anterior 

 extremity is free, and can IKS employed in prehen- 

 sion.' The peculiar prehensile power of the human 

 hand is chielly dependent upon the length, power, 

 and mobility of the thumb, which can be brought 

 into exact opposition to the extremities of all the 

 fingers, whether separately or grouped together. 



The general arrangement of tne bones or the hand 

 will l>e understood by a reference to fig. 1. 



In tig. 2 we have a diagram showing the way in 



which the bones of the hand are arranged. Die 



carpal I tones (3 to 10 in the 



n iv figure) are eight in number, 



**Q [) J and are arranged in the wrist 



' "D I] n* in two rows. The first or 



<\ 1 fl f n pper row consists practically 



,& n n "* * three bone ? (3> 4> 5)> tho 



,,0^ |_\ |_ 1 fl" fowth (6) being regarded as 

 (ft cn rj-j .-Jr belonging to the class of Sesa- 

 Q-, pb moid Bones (Q.V.), and the 

 ^-p ' second row of four bones ( 7, 

 17] 8 - 9 1); 80 tn at, excluding 

 the pisiform bone (6), the 

 ' ' carpal and the tarsal bones 

 correspond in number. As we 

 commonly term the palm the 

 front of the hand, the thumb 

 becomes conventionally the 

 outer, and the little finger the 

 inner digit ; but according to 



Fig. 2. Diagram of 



the Bones of the 



Hand, with the 



ends of the Radius 



and Ulna ( after 



Humphry) : 

 1, end of radius; 2, end *l lp ciilna of comnnrntivp"an 



of ulna : 3, scaphoid ; 4, OI . com pa r ative an- 



atomy, and in order to com- 

 pare the hand and foot, we 

 ought to reverse these terms. 



scmiltinar ; 5, cunei- 

 form ; (5, pisiform ; 7, 

 trapezium ; 8, trape- 



metacarpal bones ; 12, bones of the first row sup- 

 12. first row of pha- ports (through the interven- 



S?TiiiS;&ft# ij on 2j 7 T d 8 j i he r bones ? f 



i, thumb; ii, forefinger, t thumb and forefinger (I 

 Ac.; v, little finger. and II), and constitutes with 

 them the outer division of the 

 hand. The inner (5) of the carpal bones bears 

 the little and the next (the ring) finger (v and 

 iv), and constitutes with them the inner division 

 of the hand, while the middle one (4) bears the 

 middle finger (ill), and belongs to the middle 

 division of the hand. We likewise see from this 

 figure, and also from fig. 1, that the two outer 

 bones (3 and 4) are connected with the radius, 

 while the inner bone (5) is connected (indirectly 

 by a thick ligament) with the ulna. 



The carpal bones are so arranged that the carpus 

 presents a dorsal convex surface, upon which the 

 t -MI, Ions of the extensor muscles of the fingers 

 play, and a palmar concave surface on which the 

 tendon! of the Hexor muscles lie. The several bones 

 are joined to one another each bone being united 

 lot liree or more others by a large extent of surface, 

 and are girded together by strong ligamentous 

 bands. The wrist is thus as strong as if it had 

 been constructed of one solid piece of bone, while 

 the slight gliding movements which occur between 

 the several bones give it an elasticity which serves 

 to break the shocks that result from 'falls upon the 

 hand. The uppermost surface of the first row of 

 carpal bones is convex, and this convex surface is 

 received into a wide cup or socket, formed by the 

 lower articular surface of the radius and 'by a 

 ligament passing from that lx>ne to the ulna, tike 

 the great toe, the thumb has only two phalanges, 

 while each of the other digits has three. 



For the different directions in which the arm 

 and hand collectively can be moved, see the descrip- 

 tion of the construction and movements of the 

 shoulder and ellxnv joints at ARM. Movements 



of the forearm and hand, to which there in virtually 

 nothing analogouH in the leg, are those of 'prona- 

 tion ami summation.' In pronation (derived from 

 ]in>iinn, 'with the face downwards') we turn the 

 palm of the hand downwards, as in picking up 

 any object from the table; in mtpination (derived 

 from nujnnwi, 'with the face upwards'), we turn 

 the palm upwards, as for the purpose of receiving 

 anytning that may tie placed in it. 



These movements of pronation and supination 

 are so important to the usefulness of the hand 

 that we must notice the muscles by which they 

 are chiefly effected. One of these muscles passes 

 from a projecting process on the inner side of the 

 arm-bone at its lower end to the outer edge of the 

 middle of the radius. Its contraction causes the 

 radius to roll over, or in front of, the ulna. It thus 

 pronates the hand, and is called &pronutor muscle. 

 Another crosses from the front of the lower end of 

 the ulna to the corresponding part of the radius. 

 Its shape and its action are indicated by the 

 name pronator miadratus. Another muscle passes 

 from a projecting process on the outer side of 

 the arm-bone and from the outer aspect of the 

 ulna to the outer surface of the radius near it* 

 upper part. It runs therefore in an opposite direc- 

 tion to the former muscle, and produces an opposite 

 effect, rolling the radius and the hand back into 

 the position of supination. Hence it is called a 

 supinator muscle ( see fig. 3 ). The fourth is a very 

 powerful muscle termed the Biceps (a.v.), which 

 not only bends the elbow, but, from tne mode in 

 which its tendon is inserted into the inner side of 

 the radius, 'also rotates the 

 radius so as to supinate the 

 hand ; and it gives great 

 power to that movement. 

 When we turn a screw, or 

 drive a gimlet, or draw a 

 cork, we always employ the 

 supinating movement of the 

 hand for the purpose ; and 

 all screws, gimlets, and im- 

 plements of the like kind are 

 made to turn in a manner 

 suited to that movement of 

 the right hand, l>ecause 

 mechanicians have observed 

 that we have more power to 

 supinate the hand than to 

 pronate it.' Supination can 

 only be performed to its full 

 extent by man, and even in 

 man it is not the natural or 

 habitual position ; monkeys 

 can partially effect the move- 

 ment, and in most of the 

 lower animals the part corre- 

 sponding anatomically to the 

 hand is constantly in a state 

 of pronation. 



The movements of which 

 the hand itself, without 

 reference to the arm, are 

 capable, are very numerous, 

 and in this respect differ con- 

 siderably from the corre- 

 sponding movements of the 1, biceps; 2, tendon of 

 foot, fims we can bend the . :, 

 fingers down upon the palm, 

 or we can extend them 

 l>eyond the straight line ; we 

 can separate them from one 

 another to a considerable 

 extent, and we can close them 

 with considerable force. The wrist and hand are 

 IxMit forwards or flexed upon the forearm by three 

 mu-elos which pass downwards from the inner 



Fig. 3. The super- 

 ficial Muscles of the 

 Forearm : 



the long ]ialmar muscle, 

 sprvad ing n t ( at 9 ) into 

 the palmar fascia ; 8, the 

 ulnar flexor of the wrist : 

 10, the long supinator 

 muscle. 



