16 THE HORSE. 



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 *) 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 sym- 

 metrical arrangement of the rest of the foot around 

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

 digit (pollex or hallux) has only been found in some 

 extremely ancient and primitive forms. 



It will not be necessary to enter into any descrip- 

 tion of the remaining anatomical characters by which 

 these two groups are distinguished, although, as be- 

 fore said, they are very marked, and pervade almost 

 every portion of their organization. The differen- 



* The phalanges are the separate bones of which the dig- 

 its are composed. They are three in number in each digit, 

 called respectively first, second, and third, or proximal, mid- 

 dle, and distal ; the last being often also called "ungual," be- 

 cause 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." 



