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than thirty distinct^ species of the horse tribe, in the Tertiary 

 deposits of the West alone ; and it is now, I think generally 

 admitted that America is, after all, the true home of the Horse. 



I can offer you no better illustration than this of the advance 

 vertebrate palaeontology has made during the last decade, or of 

 the important contributions to this progress which our Kocky 

 Mountain region has supplied. 



The oldest representative of the horse, at present known, is 

 the diminutive Eohippus from the lower Eocene. Several spe- 

 cies have been found, all about the size of a fox. Like most 

 of the early mammals, these Ungulates had forty-four teeth, 

 the molars with short crOwns, and quite distinct in form from 

 the premolars. The ulna and the fibula were entire and dis- 

 tinct, and there were four well developed toes and a rudiment 

 of another on the fore feet, and three toes behind. In the 

 structure of the feet, and in the teeth, the Eohippus indicates 

 unmistakably that the direct ancestral line to the modern horse 

 has already separated from the other Perissodactyles. In the 

 next higher division of the Eocene, another genus (Orohippus) 

 makes its appearance, replacing Eohippus, and showing a 

 greater, although still distant, resemblance to the Equine type. 

 The rudimentary first digit of the fore foot has disappeared, 

 and the last premolar has gone over to the molar series. Oro- 

 hippus was but little larger than Eohippus, and in most other 

 respects very similar. Several species have been found in the 

 same horizon with Di?ioceras, and others lived during the upper 

 Eocene with Diplacodon, but none later. 



Near the base of the Miocene, in the Brontotherium beds, 

 we find a third closely allied genus, Mesohippus, which is about 

 as large as a sheep, and one stage nearer the horse. There are 

 only three toes and a rudimentary splint bone on the fore feet, 

 and three toes behind. Two of the premolar teeth are quite 

 like the molars. The ulna is no longer distinct, or the fibula 

 entire, and other characters show clearly that the transition is 

 advancing. In the upper Miocene, Mesohippus is not found, 

 but in its place a fourth form, Miohippus, continues the line. 



