CHAPTER II. 



THE HORSE AND ITS NEAREST EXISTING RELATIONS. 



The tapirs (Family Tapiridcc) — Characters, species, geograph- 

 ical and geological distribution — The rhinoceroses (Fam- 

 ily Ithinocerotid(v) — The horses (Family Equidce) — Their 

 immediate predecessors — The hipparions or three-toed 

 horses of Europe and America — Existing species of horses 

 — The horse (Equus caballus) — Wild, domesticated, and 

 feral horses — Wild asses — Equus hemionus of Asia and its 

 varieties — The African wild ass and the domestic ass 

 (Equus asinus) — Striped members of the equine family — 

 Zebras and quaggas (Equus zebra, E. burchetti, E. grcvyi, 

 and E. quagga) — Hybrids or mules — Aptitude for domes- 

 tication only found in certain members of the family. 



As shown in the last chapter, the Perissodactyle 

 ungulates, by various and gradually progressing de- 

 viations from the common original type, began at a 

 very early age to break up into several groups, some 

 of which, after undergoing a considerable degree of 

 specialization, have become extinct, without leaving 

 successors ; but three of these modified types, already 

 distinct at the close of the Eocene period, have con- 

 tinued up to the present day, gradually, as time ad- 

 vanced, becoming more and more divergent from each 



