UNGULATES, OR HOOFED QUADRUPEDS 349 



except for a patch of whitish colour on the back in the region 

 of a gland, which seems to spread out and become more noticeable 

 when the little animal is enraged. There are four toes on the front 

 limbs and three on the hind. 



The Odd-Toed Ungulates, or Perissodactyla, may be grouped 

 in three living families (i) The Equidcs, or Horses (including the 

 asses and zebras) ; (2) the Tapirida, or Tapirs ; (3) the Rhino- 

 cerotidce, or Rhinoceroses. 



All the existing and some of the extinct members of the Horse 

 family (Equidce) are characterised by the feet being formed of 

 one perfectly developed digit or toe only, the other toes being 

 present in a rudimentary shape as the splint bones. Thanks to 

 the discovery of abundant and very perfect fossil remains in various 

 strata, it has been possible to trace, step by step, the ancestry and 

 evolution of the modern Horse, from a five-toed ancestor called the 

 Phenacodus that lived during the Eocene period of the earth's 

 geological history. The true Horses are represented by one well- 

 established species, Equus caballus, from which all the other races 

 or varieties are descended by a process of selection under the care 

 of man, and these vary in size, proportion of parts, and colour, 

 as much as any two closely allied species of wild animals can be 

 said to be defined from each other. Darwin considered that no 

 aboriginal or truly wild Horse is positively known to exist, for 

 the so-called " Wild Horses " of the East may probably be descended 

 from those which have escaped from the service of man. In all 

 probability the truly wild Horse has been exterminated by the 

 hand of man in those countries which it formerly inhabited, and 

 in which it has left its remains to attest its former presence. 



Sir W. Flower in his book on "The Horse" states that he 

 considers that " the nearest approach to truly wild Horses existing 

 at present are the so-called tarpans, which occur in the steppe 

 country north of the Sea of Azov, between the river Dnieper and 

 the Caspian. They are described as being of small size, dun colour, 

 with short mane and rounded obtuse nose." The genus Equus 

 includes the Horse, the Asses, and the Zebras. 



The different varieties of the Horse are so well known as to 

 call for no special mention here ; indeed, to describe them 

 adequately would require more space than the whole of the present 

 volume. Of the Wild Asses, opinions differ regarding the number 



