OEDEK OF EODENTIA. 



This Order is one of the most extensive in the class of Mammals, 

 and includes certain animals of small or moderate size, the dis- 

 tinctive characteristic of which is, that they possess only two kinds 

 of teeth — incisors and molars. The incisors, two in number, in 

 front of each jaw, are very remarkable. Their office is to cut, 

 as with shears, roots and branches, and they are wonderfully 

 constructed for attaining this result. These teeth are long, 

 curved, and stout, and being covered with enamel on their front 

 face only, they wear away more behind than in front, and, 

 by rubbing one against the other, naturally form a bevelled 

 edge. This is a very advantageous arrangement, as thus the 

 teeth always present a sharp-cutting and very hard edge, well 

 adapted for sawing through or gnawing tough substances. By a 

 phenomenon which can hardly excite too much admiration, the 

 incisors always maintain the same length, notwithstanding their 

 continual wear. The fact is, that they have no roots, and grow 

 from the base in the same proportion as they are worn awaj' at 

 the top. It is thus explained why it is that when one of the 

 incisors happens to break, the one ojaposite to it grows to an 

 indefinite extent and becomes distorted in shape. 



The molars are separated from the incisors by an emptj' space. 

 In each jaw there are never less than three pairs nor more than 

 six pairs of molar teeth. In most cases, the enamel forms wrinkles 

 on their surface of varied shapes, which gives them an uneven 

 appearance, and causes them to act as a kind of rasp, which much 

 facilitates mastication. 



Animals of the Eodent Order feed on seeds, fruit, leaves, and 

 grasses, occasionally on roots and bark. Some of them, however, 

 such as Rats, are omnivorous, and will eat even putrefied flesh ; 



