ORDER OF RODENTIA. 
This Order is one of the most extensive in the class of Mammals, 
and includes certain animals of small or moderate size, the dis- 
tinctive characteristic of which is, that they possess only two kinds 
of teeth — incisors and molars. The incisors, two in number, in 
front of each jaw, are very remarkable. Their office is to cut, 
as with shears, roots and branches, and they are wonderfully 
constructed for attaining this result. These teeth are long, 
curved, and stout, and being covered with enamel on their front 
face only, they wear away more behind than in front, and, 
by rubbing one against the other, naturally form a bevelled 
edge. This is a very advantageous arrangement, as thus the 
teeth always present a sharp-cutting and very hard edge, well 
adapted for sawing through or gnawing tough substances. By a 
phenomenon which can hardly excite too much admiration, the 
incisors always maintain the same length, notwithstanding their 
continual wear. The fact is, that they have no roots, and grow 
from the base in the same proportion as they are worn away at 
the top. It is thus explained why it is that when one of the 
incisors happens to break, the one opposite to it grows to an 
indefinite extent and becomes distorted in shape. 
The molars are separated from the incisors by an empty space. 
In each jaw there are never less than three pairs nor more than 
six pairs of molar teeth. In most cases, the enamel forms wrinkles 
on their surface of varied shapes, which gives them an uneven 
appearance, and causes them to act as a kind of rasp, which much 
facilitates mastication. 
Animals of the Bodent Order feed on seeds, fruit, leaves, and 
grasses, occasionally on roots and bark. Some of them, however, 
such as Bats, are omnivorous, and will eat even putrefied flesh ; 
