12 
MAMMALS. 
(cement). Such a model will enable us to understand the nature of the cheek-teeth 
of the Ungulate Mammals when we come to them. 
Importance Of From a utilitarian point of view Mammals are of extreme 
Mammals importance to man, since it is from them—and more especially from 
to Man. the Ungulate order—that by far the greater part of his animal food 
is procured, while their skins or fur furnish him largely with raiment; and it is 
from their ranks alone that all his beasts of burden and draught are recruited. 
Moreover, since these creatures are the highest representatives of the animal 
kingdom, among whom man himself must, from a zoological standpoint, be 
included, their study is one which commends itself most forcibly to all who are 
in any way interested in Natural History. 
Mammals in Numerous as are the Mammals now living, it must never be 
the Past. forgotten that they form but a small moiety of those which flourished 
at earlier periods of the history of our earth. The Mammals of the present day 
may, indeed, be compared to the topmost branches and twigs of a giant forest tree, 
of which the larger limbs and trunk are concealed from our view. And it will 
accordingly be manifest that any one who confines his studies to the existing species 
will have but a very imperfect idea of the whole array of Mammalian life, and of 
the mutual connection of its various branches. The study of fossil Mammals is, 
however, a difficult one, and one requiring an extensive knowledge of comparative 
anatomy. All that can, therefore, be done in a work of the present nature is to 
call attention, as occasion arises, to some of these extinct Mammals which are of 
especial importance and interest as showing the manner in which groups now widely 
separated from one another were formerly more or less completely connected. 
Although the number of 
extinct Mammals is very large, 
yet by far the greater propor¬ 
tion of these belong to the 
latest of the three great epochs 
into which the geological his¬ 
tory of our globe has been 
divided. Whereas, during 
the long-past epoch known as 
the Secondary period, during 
which our chalk and oolites were deposited, the earth was tenanted by gigantic 
reptiles of strange form, it is not till we come to the rocks overlying the chalk, 
such as the London clay and overlying strata, that we find Mammals taking an 
important place among the inhabitants of the earth. It was, indeed, during this 
so-called Tertiary period that these animals attained the dominant position which 
they now occupy; and the present stage of the earth’s history may be truly called 
the age of Mammals and Birds. We are not, however, to suppose from this that 
Mammals were unknown before the Tertiary period; a considerable number of 
species, mostly of small size, having been already discovered. 
An additional importance attaches to the study of extinct Mammals, since it is 
THE LEFT HALF OF THE LOWER JAW OF AN EXTINCT POUCHED MAMMAL. 
From the Cretaceous Rocks of North America. The tusk is 
marked a .—After Marsh. 
