OSTEOLOGY AND ARTHROLOGY 37 



the ulna tends to disappear ; the hand becomes less and less 

 suitable for grasping, climbing, or digging, so as to form 

 an organ exclusively adapted for walking and supporting 

 the body. 



Thus, the bear (plantigrade) has five digits, and the 

 power of performing the movements of supination and 

 pronation. Indeed, we know with what facility this animal 

 is able to move his paws in every direction, and climb a tree 

 by grasping it with his fore-limbs. It is well known, 

 however, that no animal except the ape can perform the 

 movements of rotation of the radius around the ulna 

 with the same facility as man ; and that none possesses the 

 same degree of suppleness, extent, and variety of move- 

 ments of the forearm and hand. 



In the digitigrades there is one finger which is but slightly 

 developed, and which is always removed from the ground — 

 that is, the thumb : there is also a little less mobility of the 

 radius around the ulna. 



In the ungulates the limbs are simply required to 

 perform the movements of walking, and form veritable 

 columns of support, which become the more solid as 

 they are less divided. The bones of the forearm are fused 

 together ; there is therefore no possibility of rotation 

 of the radius around the ulna. The metacarpus is 

 reduced to a single piece, which in the horse consti- 

 tutes what is known as the canon. The number of digits 

 becomes diminished, so that in ruminants there are not 

 more than two, and in the horse but one. We should, 

 however, add that, up to the present, we have taken into 

 account only perfect digits, those that rest on the ground. 

 We shall see further on that there exist supplementary 

 digits, but that they are only slightly developed, and are 

 represented in some cases by mere osseous spurs ; it is this 

 fact that has permitted us to ignore them in the general 

 study which we have just made. 



Because, as we have already said, the unguligrades have 

 the inferior extremity of the digit encased in a horny sheath, 

 which forms the hoof of the horse and the corresponding 

 structures [onglons) in the ox, those animals have been 



