FOSSIL HORSE. 393 



ever, from this in the form of the fifth or internal prism of 

 dentine (m) in the upper molars, and in its continuation 

 with the anterior lobe* of the tooth ; the fifth prism being 

 oval and insulated in the Equus primigenius of v. Meyer. 



The Oreston fossil teeth, which in their principal 

 characters manifest so close a relationship with the miocene 

 Equus primigenius, differ, like the later drift species (Eq. 

 fossilis), from the recent Horse in a greater proportional 

 antero-posterior diameter of the crown of the second upper 

 molar, and also in a less produced anterior angle of the first 

 molar, as shown by the tooth figured in cut 152, as con- 

 trasted with the corresponding one of the recent Horse 

 (fig. 151.) 



Fig. 153 illustrates the charac- *& 153 - 



ter, above adverted to, of the 

 complex plication of the enamel, 

 as it appears on the grinding sur- 

 face of a partially worn upper 

 molar tooth, the second of the right 

 side : the length of this tooth is 

 three inches four lines, and the 



fangs had not begun to be formed. 2nd molar, upper jaw, nat. 

 f. . , , , , r> i -t size, Equus plicidens, Oreston. 



One cannot view the elegant fold- 

 ings of the enamel in the present fossil teeth, and in those of 

 the move ancient primigenial species (Hippotheria) of the 

 continental miocene deposits, without being reminded of the 

 peculiar character of the enamel of the molar teeth of the 

 Elasmotherium, in which it is folded in elegant festoons. 

 This extinct pachyderm, which surpassed the Rhinoceros 

 in size, resembled that genus very closely in the general 

 disposition of the folds of enamel in the grinding teeth, but 

 agreed with the genus Equus in the deep implantation of 

 those teeth by an undivided base. The Elasmothere 



