62 CLASS MAMMALIA. 



rongeurs, from the verb ronger, which bears the 

 same signification. Thus it is that they attack with 

 success the hardest substances, and frequently feed 

 on wood and the bark of trees. The better to fulfil 

 this object, these incisors have no enamel except in 

 front, so that their posterior edge wears out sooner 

 than the anterior. Their prismatic form causes 

 them to grow from the root in proportion as they 

 wear from the edge, and this disposition to grow is 

 so powerful, that if one of them is lost or broken, 

 the opposite one having nothing any longer to 

 comminute, becomes most prodigiously developed. 

 The lower jaw is articulated by a longitudinal con- 

 dyle, so that it has no horizontal motion, except 

 from rear to front, and vice versa, as is suitable for 

 the action of gnawing. The molars, likewise, have 

 flat coronals, the enamelled eminences of which 

 are always transversal, to be in opposition to the 

 horizontal motion of the jaw, and better answer 

 the purposes of trituration. 



Those genera, in which these eminences are simple 

 lines, and where the coronal is perfectly plane, are 

 more exclusively frugivorous. Those which have 

 the eminences of their teeth divided into smooth tu- 

 bercles, are omnivorous. Finally, the small number 

 of those which have points, attack other animals 

 more readily, and approach a little to the Carnas- 

 siers. 



The form of body in the Rodentia is generally 

 such, as that the hinder part of the body and limbs 

 exceed the front, so that they may be said to leap 



