678 THE POPULAR SCIENCE MONTHLY. 



came extinct, leaving apparently no successor, unless possibly we 

 have in the Proboscidians their much-modified descendants. Their 

 genetic connection with the Coryphodonts is much more probable, in 

 view of what we now know of the two groups. 



Besides these peculiar mammals, which are extinct, and mainly of 

 interest to the biologist, there were others in the early Tertiary which 

 remind us of those at present living around us. When a student in 

 Germany some twelve years ago, I heard a world-renowned Professor 

 of Zoology gravely inform his pupils that the horse was a gift of the 

 Old World to the New, and was entirely unknown in America until 

 introduced by the Spaniards. After the lecture I asked him whether 

 no earlier remains of horses had been found on this continent, and 

 was told in reply that the reports to that effect were too unsatisfac- 

 tory to be presented as facts in science. This remark led me, on my 

 return, to examine the subject myself, and I have since unearthed, 

 with my own hands, not less 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 ver- 

 tebrate paleontology has made during the last decade, or of the 

 important contributions to this progress which our Rocky Mountain 

 region has supplied. 



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

 diminutive Eohippus, from the lower Eocene. Several species have 

 been found, all about the size of a fox. Like most of the early mam- 

 mals, 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 distinct, 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, OroMppus, makes its appear- 

 ance, replacing Eohippus, and showing a greater, although still dis- 

 tant, 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. OroMppus was but little larger than Eohippus, and 

 in most other respects very similar. Several species have been found 

 in the same horizon with Dinoceras, and others lived during the upper 

 Eocene with Diplacodon, but none later. 1 



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 



1 Since this address was delivered, I have found in the Diplacodon beds a new genus 

 of Equines {Ejnhippus), which is larger than OroMppus, and has the same number of toes, 

 but has two premolar teeth like the molars. 0. C. M. 



