32 



This genus is near the Anchitherium of Eiyope, but presents 

 several important differences. The three toes in each foot are 

 more nearly of a size, and a rudiment of the fifth metacarpal 

 bone is retained. All the known species of tins genus are larger 

 than those of Mesohippus, and none pass above the Miocene. 



The genus Protohippus of the lower Pliocene, is yet more 

 equine, and some of its species equaled the ass in size. There 

 are still three toes on each foot, but only the middle one, cor- 

 responding to the single toe of the horse, comes to the ground. 

 This genus resembles most nearly the Hipparion of Europe. 

 In the Pliocene, we have the last stage of the series before 

 reaching the horse, in the genus Pliohippus, which has lost the 

 small hooflets, and in other respects is very equine. Only in 

 the upper Pliocene, does the true Equus appear, and complete 

 the genealogy of the Horse, which in the Post-Tertiary roamed 

 over the whole of North and South America, and soon after 

 became extinct. This occurred long before the discovery of 

 the Continent by Europeans, and no satisfactory reason for the 

 extinction has yet been given. Besides the characters I have 

 mentioned, there are many others, in the skeleton, skull, teeth, 

 and brain of the forty or more intermediate species, which 

 show that the transition from the Eocene Eohippus to the 

 modern Equus, has taken place in the order indicated, and I 

 believe the specimens now at New Haven will demonstrate 

 the fact to any anatomist. They certainly carried prompt 

 conviction to the first of anatomists, who was the honored guest 

 of the Association a year ago, whose genius had alreadj r indi- 

 cated the later genealogy of the horse in Europe, and whose 

 own researches so well qualified him to appreciate the evidence 

 here laid before him. Did time permit, I might give you at 

 least a probable explanation of this marvellous change, but 

 justice to the comrades of the horse in his long struggle for 

 existence demands that some notice of their efforts should be 

 placed on record. 



Beside the Horse and his congeners, the only existing Peris- 

 sodactyles are the Rhinoceros and the Tapir. The last is the 



