250 ORDER RODENTIA ; GENERAL CHARACTERS. 



hand, but by holding it between the two paws, as seen in 

 Fig. 48. 



218. The principles upon which the division of this order into 

 families should be founded, have not yet been satisfactorily 

 established. It is convenient, however, to distribute them in the 

 first instance into two sections ; of which the first, possessing 

 clavicles, includes the Squirrels, Mice, and Beavers ; whilst to 

 the second, in which the clavicles are nearly or completely 

 absent, belong the Porcupines, Hares, and Guinea-pigs. The 

 three principal families constituting the first section, may be 

 distinguished by the form of the tail, and the number of the 

 molar teeth. In the SCIURID^J, or Squirrel tribe, the tail is 

 large and bushy ; and the molar teeth are four on each side, with 

 a fifth in the upper jaw, which soon drops out. The MURID^E, 

 or Mouse and Rat tribe, have a round scaly tail, and only three 

 molars on each side. The family CASTORIOE, which includes 

 none but the Beavers^ is at once distinguished by the peculiar 

 flattening of the tail, which is covered with scales ; there are four 

 molars on each side. Between the two last families may be 

 placed the group of ARVICOL^J, or Voles, which include many 

 species that are commonly termed Rats and Mice ; but these are 

 distinguished by a peculiarity in their teeth, that indicates a 

 greater affinity to the Beavers, with which they are classed by 

 some Naturalists. It is remarkable that the Rodents of this 

 series should be much more extensively diffused over the globe, 

 than those of the families hereafter to be described. There is no 

 part in which some kinds of Mice and Rats are not to be found ; 

 and Squirrels are as widely diffused, with the exception of New 

 Holland. The order is most abundant in temperate regions, the 

 reverse of which is the case, in regard to Mammals of large size. 

 . 219. The family SciURiD^a, or Squirrel tribe, contains a large 

 number of species, many of which bear a strong resemblance to 

 each other. Some of them, like the common Squirrel of this 

 country, (Fig. 48,) have a very extensive range, and are liable 

 to undergo great alterations in colour. The form of this little 

 animal is sufficiently well known, to render a particular descrip- 

 tion of it unnecessary. Living entirely upon vegetable food, 



