214 DOMESTICATED ANIMALS AND PLANTS 
We know that several horselike forms developed in South 
America, but that all perished for one cause or another, one at 
least from soft teeth. It is exceedingly remarkable that while 
the North American horse progressed almost up to the modern 
Fore Foot Hind Foot Teeth 
One Toe One Toe 
Splinis of Splints of 
2nd and 4th| [| 2ndand 4th Bg 
digits digits Long- 
Crowned, 
Cement- 
Three Toes Three Toes covered 
Side toes Side toes 4 es) 
not touching not touching| 
the ground the ground 
Three Toes 
Side toes Y 4 
touching the Three Toes 
Mesohippus grounds | Side toes 
IPP Splint of 5thdigit seaenenaaie Short- 
ground S| Fi Crowned, 
aay 8) without 
Four Toes 
Protorohippus Cement 
easy Four Toes Three Toes 
Hyracotherium h Splint of Splint of ¥Y @ 
(Eohippus) Ist digit Sth digit 
Fic. 38. Comparative drawings of skulls, feet, and teeth of prehistoric horses, 
showing evolutionary development. Reproduced, by permission, from “Origin 
and History of the Horse,” by H. F. Osborn 
type,! he became extinct for some reason, and, so far as we know, 
before he was ever domesticated. 
What caused this extinction here and yet preserved the 
Asiatic form till man came upon the earth we cannot, with our 
present knowledge, even conjecture; though it is known that the 
1 He had reached the size of the Shetland pony with three toes, only one 
of which rested firmly on the ground, digits II and IV being much like the 
“dew claws” (digits II and V) of pigs; digits I and V being represented by 
“splints” (digits numbered I-V beginning on the inside). 
