166 



THE RODENTS. 



ders above the surface in such a manner that it bears some resemblance 

 to a human beino^. 



The Manatee [Munatus Australis). 



EODENTS. 



The Rodents, or gna\Ying animals, derive their name from the pe- 

 culiar structure of their teeth, which are specially fitted for gnawing 

 their way through hard substances. The jaws of the Rodents are 

 heavily made, and very large in proportion to the head, their size 

 being needful not only for the support of the gnawing teeth, but for 

 their continual development. There are no canines, but a wide gap 

 exists between the incisors and the molars, which are nearly flat on 

 their surfaces, and are well suited for grinding the soft substances on 

 which these animals feed. 



The structure of the chisel-edged incisor teeth is very wonderful, and 

 may be easily understood by inspecting the teeth of a rat, mouse, hare, 

 or rabbit. 



As the teeth are continually worn out by the severe friction which 

 they undergo unceasingly, there must needs be some provision for re- 

 newing their substance, or the creature would soon die of starvation. 

 In order to obviate this calamity, the base of the incisor teeth pass 

 deeply into the jaw-bone, where they are continually nourished by a 

 kind of pulpy substance from which the tooth is formed, and which 

 adds fresh material in proportion to the daily waste. 



vSomething more is needed for the well-being of the animal than the 



