394 SOLIPEDIA. 
appears, therefore, to have formed one of the links, now 
lost, which connected the Horse with the Rhinoceros, and 
it is interesting to observe that some of the extinct species 
of Horse, m the analogous complexity of the enamel folds, 
more closely resembled the Elasmothere than do the pre- 
sent species. 
The canines are small in the Horse, 
Fig. 154. 
and rudimental in the Mare. I figure 
here the fossil right lower canine of a 
colt, found in the same cavernous fissure 
(s) as the plicident molars, and proba- 
bly, therefore, belonging to the same 
species: the view of the inner side, given 
in fig. 154, shows the folding in of the 
anterior and posterior margins of the 
crown, characteristic of the canines of 
the genus Hguus, and which is very 
well marked in the present specimen. 
The incisors associated with the plici- 
Lower canine tooth, 
nat. size, Equus plicidens, 
Oreston. 
dent molars offered no distinctive cha- 
racters. 
Some of the bones ef the extremities of the fossil Horse 
from the same fissure (8) of the Oreston Caves, indicate an 
animal about thirteen hands and a half high. The astra- 
galus, reduced in fig. 155, one third the natural size, is a 
yery characteristic bone of the present genus ; the upper 
articular surface, which is here represented, is oblique, and 
the two convex ridges are divided by an unusually deep, 
almost angular, valley; the articular pulley, or trochlea, in 
the lower end of the tibia has, of course, a corresponding form 
—the cavities and eminences being reversed ; by the depth 
and obliquity of these, the tibia and astragalus of the Horse 
may readily be distinguished from those bones in any other 
