a 
RODENTIA. 135 
length is so powerful, that if one of them be lost or broken, 
its antagonist in the other jaw having nothing to oppose or 
comminute, becomes developed to a most monstrous extent. 
The lower jaw is articulated by a longitudinal condyle, in 
such a way as to allow of no horizontal motion, except from 
back to front, and vice versa, as is requisite for the action of 
gnawing. The molars also have flat crowns, whose enamelled. 
eminences are always transverse, so as to be in opposition to 
the horizontal motion of the jaw, and to increase the power of . 
trituration. 
The genera in which these eminences are simple lines, 
and the crown is very flat, are more exclusively frugivorous ; 
those in which the eminences of the teeth are divided into 
blunt tubercles are omnivorous; while the small number of 
such as have no points saore readily attack other animals, and 
approximate somewhat co the Carnaria. 
The form of the body in the Rodentia is generally such, 
that the hinder party of it exceed those of the front; so that 
they rather leap than walk. In some of them this dispropor- 
tion is even as excessive as it is in the Kanguroos. 
The intestines of the Rodentia are very long; their stomach 
simple, or but little divided; and their cecum very volumi- 
nous, even more so than the stomach. In the subgenus My- 
oxus, however, this intestine is wanting. 
In the whole of this class the brain is almost smooth and — 
without furrows; the orbits are not separated from the tem- 
poral fosse, which have but little depth, and the eyes are al- 
together directed laterally. The zygomatic arches, thin and 
curved below, announce the weakness of the jaws; the fore- 
arms have nearly lost the power of rotation, and their two 
- bones are often united; in a word, the inferiority of these ani- 
mals is visible in most of the details of their orgamiation. 
Those genera however which possess stronger clavicles have 
a certain degree of dexterity, and use their fore feet to con- 
_ vey their food to the mouth. 
Some of them even climb with facility: such is the 
is 
Li uation «4 
