Introduction 
are sometimes immensely developed so as to form apparently 
another section to the leg, as we see in the horse and cow 
where these bones are so long that the heels on the hind feet 
are elevated a foot or more in the air. In these animals there 
is also a reduction in the mumber of toes and we find that such 
of these metacarpal and metatarsal bones as remain are fused to- 
gether, while those belonging to the missing toes are mere abor- 
tive splints. 
With these brief explanations we shall be better able to un- 
derstand the preceding table of the mammalian orders and the 
further classification which follows. 
Limits of the Work 
So easily are mammals affected by their surroundings that 
we find that differences in climate, temperature, humidity, food, etc., 
are immediately reflected in a difference in the size, colour, or 
skeletal characters of the individuals of a certain region. This re- 
sults in an immense number of geographic varieties of nearly all 
kinds of mammals which have been carefully studied and sepa- 
rated by systematic zoologists. 
The differences which distinguish these varieties are not al- 
ways perceptible to the popular eye, but as everyone wishes to be 
as nearly accurate as possible, we have mentioned in the following 
pages every species and variety of mammal found in North Amer- 
ica east of the Mississippi, and all the varieties of big game animals 
north of Mexico. Of other mammals from the West, however, only 
the most important species are described. 
The scientific names used are those adopted in the most 
reliable systematic monographs of the day and no attempt has 
been made to solve the vexed question of what constitutes a 
species and what a subspecies. Those animals which would be 
most readily recognized as different by one beginning the study 
of our mammals are separately described, while geographical races 
and closely allied species are grouped together at the end of the 
account with their range and a few of their most obvious dif- 
ferential characters. It will therefore be understood that in so 
grouping them there is no intention to reduce their taxonomic 
rank, but simply to arrange them so that the general reader, who 
does not wish to study in detail the structure of every form, 
XXil 
