ey. : 893 
FOSSIL HORSE. JIO 
ever, from this in the form of the fifth or internal prism of 
dentine (az) in the upper molars, and in its continuation 
with the anterior lobe of the tooth; the fifth prism being 
oval and insulated in the Hyuus primigenius of v. Meyer. 
The Oreston fossil teeth, which in their principal 
characters manifest so close a relationship with the miocene 
Equus primigenius, difter, like the later drift species (Z7. 
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 
(igs 151.) 
Fig. 153 illustrates the charac- Fig. 158. 
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. j 2nd molar, upper jaw, nat. 
One cannot view the elegant fold- “”” fea 10 net 
ings of the enamel in the present fossil teeth, and in those of 
the more 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 Hguus in the deep implantation of 
those teeth by an undivided base. The Elasmothere 
