386 SOLIPEDIA. 
similar character appears to have been recognized by 
M. H. v. Meyer in some of the fossil equine teeth from the 
Eppelsheim sand, since he cites the Hywus angustidens as 
a synonyme of the species which he subsequently described 
under the name of Hqwus asinus primigenius.* 
The upper molar teeth of the Horse resemble those of 
the Paleeotherium in the two deep longitudinal channels (7 
d, fig. 148,) which traverse their outer side, but the enamel- 
linings of those channels are not produced into points on 
the grinding surface. This surface of the equine molar 
also presents a close analogy with that of the Rhinoceros ; 
to aid in tracing which, the corresponding but modified 
folds and islands of enamel in the complex molar of the 
Horse (fig. 143) are marked with letters corresponding 
with those on the upper molar of the Rhinoceros lep- 
torhinus (fig. 141). For the details of the character- 
istic structure of the teeth of the genus Hqwus, which 
would be unsuited to the present work, I must refer the 
reader to the ‘ Ossemens Fossiles, and to my ‘ Odon- 
tography’; and here merely add, that the character by 
which the Horse’s molars may best be distinguished from 
the teeth of other Herbivora, corresponding with them 
in size, is the great length of the tooth before it divides 
into fangs. This division, indeed, does not begin to take 
place until much of the crown has been worn away; and 
thus, except in old Horses, a considerable proportion of 
the whole of the molar is implanted in the socket by an 
undivided base. In an old molar with roots, the pattern 
of the grinding surface, as it is shown in the figs. 142 
and 143, is a little changed by partial obliteration of the 
enamel folds, but enough generally remains to serve, 
with the form of the tooth, to distinguish it from the 
rooted molar of a Ruminant. 
* ¢ Paleeologica,’ p. 80. 
