96 CLASS MAMMALIA, 



SUPPLEMENT TO THE RODENTIA. 



The leading physical character which distinguishes the 

 order Rodentia, and from which indeed it receives its name, 

 is that of dentition, fitted for the operation of gnawing. 

 The order has been called Rosores, by Stor, and Prensicu- 

 lantia, by Illiger, and it corresponds with the Glires of Lin- 

 naeus, so named from one of the genera included in it. 



The Rodentia have two principal incisive teeth in each 

 jaw, which are very large, long, and generally bent, with 

 the anterior face in some species flat, in others, subcylin- 

 drical. These teeth being exposed by the habit of the 

 animal to frequent and almost constant friction against 

 substances often of considerable hardness, yield in time to 

 this reiterated operation, and wear away ; but the Creator, 

 ever willing to relax in those general laws subject to which 

 his works are constituted, when the necessities of a parti- 

 cular race of creatures may require an exception, has pro- 

 vided that these teeth, as they are exposed to wear, shall 

 be also capable of renovation* 



The incisors when they spring from their alveoli are 

 pointed, and grow from the lower part of their posterior 

 side in proportion as they wear away above ; their anterior 

 face is covered with a thick hard enamel, and as the detri- 

 tion is always oblique, the teeth preserve, in the upper 

 jaw at least, a constant sharp edge of enamel. 



To supply matter for this continued detrition, the em- 

 bedded portion of each incisor, which is not an indurated 

 root, but a mere gelatinous pulp, is much enlarged, and 

 extends in a curve above the upper and beneath the lower 

 cheek-teeth, behind those of the cheek-teeth . In the upper 



