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CHAPTER V 



DIVISION I. -VERTEBRATES, 



CLASS I. — MAMMALS. 

 ORDER III. QUADRUPEDS. 



Sub- Order. — Clawed Quadrupeds. 



INSECT-EATING, GNAWING, TOOTHLESS, AND POUCHED 

 QUADRUPEDS. 



The Insectivora are generally small animals, and so called 

 because they feed principally upon insects. Many of them pass 

 the winter in a state of lethargy, and during summer they lead a 

 secluded, nocturnal, or subterranean life. Their limbs are short, 

 and their motions very feeble. Among the most worthy of notice 

 are the hedgehog, the shrew-mouse, and the mole. 



The Rodentia, or Gnawers, are distinguished by the pos- 

 session of two large incisive teeth in the centre of each jaw, and 

 by the absence of canine teeth. There is a wide space between 

 the incisors and the molars, which last are broad, and evidently 

 calculated for the mastication of vegetable food. This arrangement 

 of their teeth remarkably qualifies them for gnawing, and enables 

 them to penetrate very solid substances; and frequently they feed 

 upon woody fibres and the bark of roots and trees. There is an 

 additional circumstance in the structure of their, incisive teeth, 

 which adapts them, to the use for which they are intended. They 

 are furnished with enamel only upon their front surface, so that 

 the back part, being merely bone, is by gnawing worn away faster 

 than that in front, and of course the front edge is kept sharp and 

 fit for cutting. To remedy the loss of substance, which is necessarily 

 continuous, there is a provision by which a constant growth takes 

 place from the root ; so that if one of these teeth is lost bv acci- 



