42 CLASS I. MAMMALIA. ORDER IV. RODENTIA. 



They are easily tamed, and become attached to those who 

 feed them. Their head somewhat resembles that of the dog. 

 They live together in large herds or families, and are valua- 

 ble as objects of trade on account of their skins and oil. 



IV. Rodentia, the 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 molares, which last are broad, 

 and evidently calculated for the mastication of vegetable 

 food. This arrangement of their Jeeth 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 circum- 

 stance in the structure of their incisive teeth, which adapts 

 them to the use for which they are intended. They are fur- 

 nished 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 necessarily takes place, there is a provision by which 

 a constant growth takes place from the root ; so that if one 

 of these teeth is lost by accident, that which corresponds to 

 it in the opposite jaw, being no longer worn away by use, in- 

 creases to a great length. Their feet are furnished with toes 

 and nails, and their hind legs are stronger and longer than 

 their fore legs ; so that frequently they leap better than they 

 run. Of this order, among others, are the beaver, the squir- 

 rel, the dormouse, the marmot, the hamster, the mouse and 

 rat, the jerboa, the various species of hare and rabbit, and the 

 porcupine. 



The Beavers (Castor fiber) have been long celebrated for 

 the value of their skins as an article of commerce, and for the 

 wonderful sagacity and forethought which they exhibit in the 

 construction of their dwellings. Their cutting teeth are 

 very strong and sharp, and they are able, with them, to fell 

 lofty trees.* They are possessed of a large, long, and broad 



* In felling a tree, several beavers are engaged at once around its trunk, and they 

 pnaw it carefully in such a part of the circumference, as will cause it to fall in a 

 direction convenient for their purposes. An observer of them relates, that he wit- 

 nessed three beavers occupied in cutting round a tree; that, after a certain period, 

 one of them left the two others, and went to a considerable distance, where ha 

 quietly watched their operations ; and that, when the trunk was nearly divided, so 

 that the weight of the branches was sufficient to bring down the tree, and the in- 

 clination was obvious on lookitrg at its summit, he gave a smart stroke with his 

 tail upon the water, as a signal to his companions, who immediately ran off with 

 jreat expedition to escape the impending danger. Long's Expedition. 



