THE 1!( INKS AND JOINTS. 



the posterior extremity of the ulna, and passes to the sharp palmar 

 ridge of the os pyramidale, where it is attached, and is inserted into 

 the os capitalo-Jiamatum ; the second ligament passes in a similar 

 manner on the palmar surface from the radius to the os "naviculare. 

 Between the two ligaments there is on the volar surface a deep 

 excavation. 



Movements of the hand. The two 

 bones of the forearm being firmly 

 united, pronatiori and supinatioii, as 

 in man, are impossible. The normal 

 position, as already remarked (see radio- 

 ulnar), is that of semi-pronation. (com- 

 pare Figs. 2 and 74). If the animal 

 be in its natural posture, with the arm 

 bent at the elbow (Fig. i), it can touch 

 the ground with the ulnar border only ; 

 but when the whole siirface of the hand 

 rests upon the ground, the action is 

 brought about as follows : the plane of 

 the carpus is in extension parallel with 

 that of the forearm ; in flexion, almost 

 at right-angles with that plane (Fig. 

 74). The os lanatum glides on the pro- 

 longation of the articular surface on. the 

 inner palmar surface of the radius, 

 while the os pyramidale is held firmly 

 by the ligament just described. The 

 hand follows the movement of the os 

 lunatum, and at the same time the three 



Bones of the forearm and hand of Rana Outer OSSa metacarpl gliding with it ill- 

 esculmta, right side, dorsum, twice nat. wa jflg the fillgei'S of the hand turn 

 size. 



inwards. 



b. The Bones of the metacarpus, ossa 

 nietacarpi (Fig. 40 ?;/). Of these there 

 are five : the second to the fifth are of 

 about equal length; the first, forming 

 t> osmuitanguiumminusortrapezoides. the rudiment of the thumb, hidden 



Ulnar portion of the radio-ulnar. , , , , . . , , 



i-v First to fifth fingers, the first only beneath the skm, is nmch shorter. 



This metacarpal bone of the thumb is 

 regarded by Duges and others as the 



first phalanx. My reason for describing it as a metacarpal has 



a Radio-ulnar. 



he Os capitato-hamatum. 



I Os lunatum. 



w Ossa metacarpi. 



Os naviculare. 



p Os pyramidale. 



r Radial portion of the radio-ulnar. 



t Os multangulum maius or trapezium. 



of two, fourth and fifth of three 



phalanges. 



