THE FORERUNNERS OF THE HORSE 265 



that Eastern Asia was the original home of the 

 horse-group ; and it derives additional importance 

 from Professor Osborn's further suggestion that 

 Pliohippus may likewise be represented in the 

 Chinese Tertiary fauna. 



The American genus Parahippus, which ac- 

 cording to Professor Osborn ranges in time from 

 the Lower Pliocene to the Upper Oligocene, 

 although Dr. Lull records it only from the Miocene 

 Loup Fork beds, has short-crowned cheek-teeth 

 resembling these of Hypohippiis in general char- 

 acters, but differing in several structural details. 

 Among these differences may be noticed the strong 

 ribbing of the external wall of the outer columns 

 of the upper milk-molars. For other details the 

 reader may refer to an article by Mr. J. W. 

 Gidley.^ Anckippodus and Desmathippus appear 

 to be synonyms of this genus. A peculiarity of 

 the short-crowned upper molars of Parahippus 

 which cannot be passed over without mention is 

 the presence in their open valleys of an exceed- 

 ingly thin layer of cement ; this being the first 

 appearance of a substance which, as shown above, 

 takes a large and important share in the structure 

 of the molars of the modern horse. This layer 

 is absent in Archcsohippus, of the Miocene of 

 Oregon, a small animal with cheek-teeth resem- 

 bling those of the undermentioned Mesohippus, but 



^ Bull. Amer. Mus. Nat. Hist., vol. xx. p. 192, 1904. 



