46 



THE BON ES AND JOINTS. 



Fiw. 40. 



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

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

 the 0* capitalo-Iiamatuni; the second ligament passes in a similar 

 manner on the palmar surface from the radius to the os navicular e. 

 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, pronation and supination, 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 j^osture, with the arm 

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

 the ground with the ulnar border only ; 

 but when the whole surface of the hand 

 rests upon the ground, the action is 

 brought about as follows : the plane of 

 the carpvis is in extension parallel with 

 that of the forearm ; in flexion, almost 

 at right-angles with that plane (Fig. 

 74). The OS lanaUim glides on the pro- 

 longation of the articular surface on the 

 inner palmar surface of the radius, 

 /? ri while the os pyramidale is held firmly 



^ ' ' by the ligament just described. The 



hand follows the movement of the os 

 Innatum, and at the same time the three 

 outer ossa meiacarpi gliding with it in- 

 wards, the fingers of the hand turn 

 inwards. 



b. The Bones of the metacarpus, ossa 

 wefacarpi (Fig. 40 m). Of these there 

 are five : the second to the fifth are of 

 about equal length; the first, forming 

 the rudiment of the thumb, hidden 

 beneath the skin, is much shorter. 

 This metacarpal bone of the thumb is 

 regarded by Dugès and others as the 

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



Bones of the forearm and liand of liana 

 escuknta, right side, dorsum, twice nat. 

 size. 



a Radio-ulnar. 



he Os capitato-Iiamatnm. 



I Os kinatum. 



m Ossa metacavpi. 



n Os navioulare. 



p Os ]iyrai)iidale. 



»• Radi:il ]icirtion of the radio-nlnar. 



t Osniultangnhim nuiiiis or trapezium. 



I' Os multanguhim minus or trapezoides. 



u Ulnar portion of the radio-ulnar. 



I -V First to fifth fingers, the first only 

 of a metacarpal, the second and third 

 of two, fourth and fifth of tliree 

 phalanges. 



