486 
UNGULATES. 
There are, however, a number of allied extinct animals which connect the true 
rhinoceroses with more generalised extinct types of Odd-toed Ungulates. Such for 
instance is the Amynodon, from the Miocene Tertiary of North America, which 
was a rhinoceros-like animal with no horn, and the full typical number of forty-four 
teeth. That is to say, there were three incisors, a tusk, and seven cheek-teeth on 
each side of both jaws; the front teeth being like those of ordinary mammals, and 
not having the peculiarly modified form presented by those of the true rhinoceroses. 
Moreover, the whole of the three upper molar teeth were alike; and none of them 
had the processes projecting into the middle valley which are found in those of all 
true rhinoceroses. Probably the Amynodon also occurred in the lower Miocene 
and upper Eocene rocks of France. There were other allied types, but the above 
example is sufficient to show that the earlier rhinoceroses were far less different 
from tapirs and some extinct generalised forms to be noticed later on than are 
their modern representatives. 
We must not, however, take leave of the rhinoceros family without referring 
to a most remarkable creature known as the elasmothere, which flourished during 
the Pleistocene period in Siberia. This creature was probably as large as Burchell’s 
rhinoceros, and like that species had no teeth in the front of the jaws. The skull 
had a bony partition in the cavity of the nose, and carried on the forehead an 
enormous protuberance which, during life, doubtless supported a horn of very large 
size. The most remarkable feature about the elasmothere is, however, to be found 
in the structure of its cheek-teeth, which while formed on the type of those of the 
rhinoceroses, are greatly elongated, and have their enamel so much folded as to 
present some resemblance to those of the horse. Indeed, the elasmothere may be 
regarded as a highly-specialised grass-eating creature, presenting a relationship to 
an ordinary rhinoceros somewhat similar to that which the horse exhibits to 
certain extinct Ungulates noticed in the sequel. 
The Horse Tribe. 
Family EQJJIDJE. 
Under the general title of horses, zoologists include not only the animals to 
which that name is restricted in ordinary language, but likewise the asses, zebras, 
and quaggas, together with certain nearly-allied extinct animals. All these are 
characterised by having very high-crowned cheek-teeth, in which the enamel is 
thrown into a series of complicated foldings, and the deep valleys between the 
component columns completely filled up with cement. In the upper cheek-teeth, 
as shown in B and C of the accompanying figure, the outer columns (pa, me) of 
each tootli are flattened, and the premolars somewhat exceed the molars in size; 
while in the lower jaw the ridges are crescent-like, although much complicated by 
the foldings of the enamel. So different, indeed, are the molars of the horses from 
those of other Odd-toed Ungulates, that it is at first sight somewhat difficult to 
realise their fundamental unity of structure. A comparison of the three figures in 
the accompanying illustration will, however, clearly indicate how the structure of 
the tall-crowned molar of the horse is essentially the same as that of the low- 
