THE STORY OF THE HORSE 231 
gap in the row of the horse’s teeth which makes it 
possible for us to insert the bit into his mouth. 
Now comes a strange accident into the life of our 
American horse. Creatures of the same kin had been 
evolving in Europe and Africa, but the developments 
are more distinctly horselike, it would seem, in our 
own country. Then for some reason the horse disap- 
peared completely from American soil. Doubtless 
two things happened. First of all, some of them mi- 
grated across a stretch of open country which then 
connected America with Asia in the neighborhood of 
Bering Strait. These creatures spread first over Asia 
and then over Africa and Europe, leaving their skele- 
tons scattered over this enormous stretch of country. 
Asses and zebras are still found abundantly and widely 
scattered, but the wild horse of to-day is seen only in 
western Asia. What happened to those who remained 
in America we shall possibly never know. Some sur- 
mise that a fly not unlike the tsetse-fly of Africa 
killed them out. Perhaps the members of the cat fam- 
ily, which are steadily growing larger and fiercer, fed 
on their young if not upon the older ones, and ex- 
terminated them. Perhaps the Glacial period which 
followed was too cold for them. But, whatever may 
have been the cause these horses died out not only in 
North but also in South America, to which country 
they had spread. 
