THE ANCESTRY OF THE HORSE 171 
developing more and more speed ; for it is a 
rule that the fewer the toes the faster the ani- 
mal: the fastest of birds, the ostrich, has but 
two toes, and one of these is mostly ornamen- 
tal; 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 repro- 
ducing a trait or feature possessed by some 
ancestor a score, a hundred, or perhaps a thou- 
sand years ago, there should reappear a char- 
acteristic of some ancestor that flourished 
100,000 years back, we should have a seeming 
abnormality, but really a case of reversion ; 
and the more we become acquainted with the 
_ structure of extinct animals and the develop- 
_ ment 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 the Hippotherium and 
