IO 
MAMMALS. 
from their relations to the temporary series of milk-teeth, to divide them into four 
distinct groups. Taking one side of the upper jaw, as that of the dog, of which the 
teeth are shown in the figure, we find the front bone, or premaxilla, carrying a small 
number (in this instance three) of simple cutting teeth, termed incisors. Behind 
these teeth, from which, as in the figure, it is generally separated by a longer or 
shorter gap, there is a tooth with a simple and often conical crown, which, like the 
incisors, is inserted in the jaw by a single root. This tooth, which is usually larger 
than the incisors, is termed the tusk, or canine tooth, and in the wild boai and 
most Carnivorous Mammals attains a very large size. It can always be distin¬ 
guished from the incisors by the fact that it is implanted in the maxilla, or second 
bone of the jaw, or at least on the line of junction between that bone and the 
premaxilla. Behind the canine we have a series of teeth, which may be as many as 
seven, although only six in the figure, with more complicated crowns, and, except the 
first, inserted in the jaw by two or more roots. This series may be collectively known 
as the cheek-teeth; but they may be divided into two minor groups according as 
to whether they are preceded by milk-teeth or not. In the dog the four teeth 
immediately behind 
the canine, with the 
exception of the first, 
are the vertical suc¬ 
cessors of milk-teeth, 
and are known as 
premolars; while the 
two hindmost teeth, 
which have no such 
temporary predeces¬ 
sors, are known as 
true molars, or molars. 
In the lower jaw the 
tooth, usually larger 
than the others, which bites in front of the upper canine is the lower canine. 
In advance of this tooth are the incisors, and behind it the premolars and molars, 
distinguished from one another in the same manner as are the corresponding teeth 
of the upper jaw. 
With the exception of the Pouched Mammals, with which we shall not have 
to deal till we come to the middle of the third volume, there are, in practically 
all the Mammals with teeth of different kinds, never more than three incisors, one 
canine, four premolars, and three molars on either side of each jaw; so that the 
total number of teeth on both sides of the two jaws is not more than forty- 
four. In the figured upper jaw of the dog the number falls short of this full 
complement, owing to the circumstance that there are only two in place of three 
molars. 
Dental As it would be exceedingly inconvenient always to have to 
Formulae. describe the number of teeth in any given Mammal by writing 
them down at length, a graphic formula has been invented by which the number 
of teeth of each species can be shortly and clearly expressed. Thus, taking 
OUTER VIEW OF THE RIGHT MILK AND 1’ERMANENT UPPER TEETH OF THE DOG. 
The lower row are the milk-teeth, and the upper the permanent 
teeth.—After Sir W. H. Flower. 
