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 more readily attack other animals, and 

 approximate somewhat to the Carnaria. 



The form of the body in the Rodentia is generally such, 

 that the hinder parts 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 crecum 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 fossae, 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 organization. 

 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 



