ITS ANCESTORS AND RELATIONS 



15 



together they form a figure symmetrically disposed to a 

 line drawn between them, and constitute the erroneously 

 called ' cloven hoof of the Ruminants, which is really 

 not one, but the two hoofs of distinct toes. These two 

 digits are always present and well developed ; the second 

 and fifth may be present in varying degrees of develop- 

 ment, or may be entirely absent ; the first is not present 

 in any known member of the group, even the most 

 ancient. 



In the Perissodactyle group, the middle or third digit 

 of both fore and hind feet is larger than any of the others, 

 and symmetrical in itself, the free border of the last bone 

 (the ungual phalanx, which supports the hoof 1 ) being 

 evenly rounded on both sides. This may be the only 

 digit sufficiently large to be of any use to the animal, 

 as in the horse, or the second and fourth may be nearly 

 equally developed on each side of it, as in the rhinoceros. 

 In the tapir and in many extinct forms, the fifth digit is 

 also present in the fore foot ; but this does not interfere 

 with the symmetrical arrangment of the rest of the foot 

 around the median line of the third or middle digit. A 



1 The phalanges are the separate bones of which the digits are 

 composed. They are three in number in each digit, called respec- 

 tively first, second, and third, or proximal, middle, and distal ; the 

 last being often also called ' ungual,' because it supports the nail or 

 hoof. The metacarpals and metatarsals are the long bones which 

 connect the carpus (wrist -bones) or tarsus (ankle-bones) with the 

 digits in the fore and hind limb respectively. When a word common 

 for both is required, they are spoken of as ' metapodials.' 



