RODENTIA. 143 



semblance. Some bear a slight likeness to the in- 

 sectivorous Carnivora, as the Mouse to the Shrew, 

 and the Porcupine to the Hedgehog ; while some 

 of the more tall and elegant of the Agoutis seem to 

 look towards the smaller Musks and Antelopes in 

 the Ruminantia. But these are the resemblances 

 of analogy, rather than of affinity. Perhaps, how- 

 ever, a true affinity exists between the Aye-aye 

 (Cheiromys* Madagascariensis), and the Quadruma- 

 na, inasmuch as it possesses thumbs to the hind 

 feet, together with other peculiarities ; and the Ca- 

 pybara leads to the Pachydermata. 



The great character of the order is, the presence 

 of two long projecting incisors in each jaw, meeting 

 in an angle, separated from the molars by a long 

 space, which is unoccupied by canines. Their func- 

 tion is as singular as their form ; it is evident they 

 are not adapted for tearing prey, nor for cropping 

 herbage ; but their office is to reduce, by continual 

 abrasion, gnawing, or nibbling, the substances on 

 which they feed, into minute atoms. They are thus 

 enabled to feed on very hard substances, such as 

 the bark of trees, and to file away the still harder 

 shells of many nuts and seeds. The incisors are 

 coated with enamel only in front ; the inner part, 

 therefore, wears down faster than the outer, and thus 

 they are always sharp, sloping with a chisel-like 

 edge. They have no roots, but grow continually ; 

 so that if one be accidentally lost, the opposite one 

 being now unworn grows out in a monstrous manner. 



* Xs/, cJieir, a hand, and ^w?, mys, a mouse. 



