276 THE DOCTRINE OF DESCENT. 
characteristics of the horse and rhinoceros with those 
of the camel. How far the latter, as ruminants, are 
directly connected with the Macrauchenide, or whether 
the form of their skull, approaching that of the horse, 
points to actual homology, it is for the present impossible 
to say. 
The Anoplotheridz are likewise distinguished by a 
sort of undifferentiated dentition, from which a number 
of specific forms might deviate in different directions. 
The Tragulide are descended from them in a direct 
line; they form a small group not unlike the musk 
animals, and are confined to South Africa and Southern 
Asia. As chewing the cud, they are more fiearly allied 
‘o the other typical ruminants with which we are ac- 
quainted ; but, on the other hand, they occupy an inter- 
mediate position towards the other non-ruminants of the 
division, of which the whole was united in the pre-historic 
world through the Anoplotheride. The Suida, or pig- 
like animals, were very profusely represented in the 
Eocene and Miocene periods. From a side branch of 
their predecessors, reaching up to the Anoplotheridz, are 
descended the river-horses, or hippopotami. The function 
of ruminating is, as we know, correlated with a complex 
structure of the stomach as well asa peculiar mechanism 
of the cesophagal groove. It is naturally impossible to 
determine in which fossil animals these arrangements 
originated ; yet it seems to have occurred at a very 
early period. Perhaps the more highly integrated struc- 
ture of some non-ruminating genera, such as the hippo- 
potamus and the peccary, may have been transmitted 
from the age of the Anoplotheride, and the very con- 
spicuous accordance of the ruminating Tragulide with 
