MAMMALIA. 445 
The genus Hipparion closely resembles the horses, but was of a much 
smaller stature. Its remains were found in the south of France. 
We have thus sketched out at some extent the history of the great group 
of pachyderms. The reasons for enumerating so many genera whose 
existence is confined to a past order of things, will appear when recapitu- 
lating the succession of the mammalia upon the surface of the earth. We 
have done this also with regard to Edentata, Marsupialia, and Cetacea. 
These groups are generally less known, and nevertheless of much greater 
importance, because they are the lowest of the class, and give us the key 
for its full understanding. 
Group 4. Ruminaniia. 
We now proceed to the group Ruminantia, through which we may pass 
more rapidly, as the families of which it is composed are generally better 
known, most of them having representatives in the fauna of the present 
day. Several genera are found in North America, some of them of quite 
imposing stature, and inhabiting the sparsely populated portions of the 
country. Some belong to the prairies, some to the forests, and others to 
the mountains. The characters of the group consist essentially in the 
singular faculty of masticating their food a second time by bringing it back 
to the mouth after a first deglutition. This power depends upon the struc- 
ture of their stomachs, of which they always have four, the three first being 
so disposed that the food may enter into either of them, the cesophagus 
terminating at the point of communication. The first, which is also the 
largest, is called the paunch, into which vegetable matters, coarsely bruised 
by a first mastication, are introduced. From the paunch they pass into 
the second, called the honeycomb or bonnet, from its peculiar structure, the 
walls being laminated like a honeycomb. ‘This second stomach is com- 
paratively very small, globular in form, and seizes the food, moistens, and 
compresses it into little pellets, which afterwards successively ascend to the 
mouth to be re-chewed. The animal remains at rest during this opera- 
tion, which lasts until all the food first taken into the paunch has been 
submitted to it. The aliment thus re-masticated descends directly into the 
third stomach called the /eaflet, on account of its walls being longitudinally 
laminated or resembling the leaves of a book; and thence to the fourth or 
the caillette, the sides of which are wrinkled, and which is the true organ 
of digestion, analogous to the simple stomach of other animals. In the 
young, as long as they subsist on the milk of the mother, the caillette is 
the largest of the four stomachs. The paunch is only developed by the 
reception of larger and larger quantities of grass, which finally give it an 
enormous expansion. 
The feet in ruminants are terminated by two toes, each cased in a hoof, 
which face each other by a flat surface, presenting the appearance of a 
single hoof which has been cleft; hence the name of cloven-footed, bifur- 
cated, &c., applied to these animals. Behind the hoof are sometimes found 
649 
