HISTORY OF THE HORSE 409 



changes and, being adapted to the new conditions, per- 

 sisted. Most fortunately, the skeletons of many of these 

 animals have been preserved, and from them it has been 

 possible to trace the evolution of various species from 

 the ancestral form down to the present day. 



History of the Horse. — The first undoubted mem- 

 bers of the horse family, which furnishes one of the best 

 known examples of a long evolutionary history, appeared 

 in North America as small animals, scarcely larger than 

 a good-sized house cat (Fig. 119). In addition to several 



Fig. 119. — Restoration of the four-toed horse; based on a mounted 

 skeleton, sixteen inches high, in the American Museum of Natural 

 History. (After C. R. Knight.) 



other remarkable characters, they had four hoofed toes 

 and a rudimentary thumb in each fore foot, while the hind 

 foot lacked the great toe and the fifth digit was small 

 and rudimentary. During the next million years, or per- 

 haps a longer period, these ancestral forms gradually be- 

 came larger and developed or evolved into (a) a relatively 

 slow-going heavy type confined to the forests, and into 

 (6) a graceful, light-bodied, swift, plains type. 



The first form became extinct after undergoing certain 

 changes, while the plains animal became differentiated 



