140 ANIMALS OF THE PAST 



Eohippus and the modern horse we can place a series of 

 animals by which we can pass by gradual stages from 

 one to the other, and that as we come upward there is an 

 increase in stature, in the complexity of the teeth, and 

 in the size of the brain. At the same time, the number 

 of toes decreases, which tells that the animals were 

 developing more and more speed ; for it is a rule that the 

 fewer the toes the faster the animal: the fastest of birds, 

 the ostrich, has but two toes, and one of^ these is mostly 

 ornamental; and the fastest of mammals, the horse, 

 has but one. 



All breeders of fancy stock, particularly of pigeons 

 and poultry, recognize the tendency of animals to 

 revert to the forms whence they were derived and 

 reproduce some character of a distant ancestor; to 

 "throw back," as the breeders term it. If now, instead 

 of reproducing a trait or feature possessed by some 

 ancestor a score, a hundred, or perhaps a thousand years 

 ago, there should reappear a characteristic of some 

 ancestor that flourished 100,000 years back, we should 

 have a seeming abnormality, but really a case of rever- 

 sion; and the more we become acquainted with the 

 structure of extinct animals and the development of 

 those now living, the better able are we to explain these 

 apparent abnormalities. 



Bearing in mind that the two splint bones of the 

 horse correspond to the upper portions of the side toes of 

 Merychippus and Mesohippus, it is easy to see that if 

 for any reason these should develop into toes, they 

 would make the foot of a modern horse appear like that 

 of his distant ancestor. While such a thing rarely 

 happens, yet now and then nature apparently does 

 attempt to reproduce a horse's foot after the ancient 

 pattern, for occasionally we meet with a horse having, 

 instead of the single toe with which the average horse is 



