128 



CHARACTERS OF VERTEBRATE ANIMALS 



even in Australia, from which all the other groups are absent. 

 The tail is bare and scaly, the incisor teeth narrow, and the 

 fore- and hind-limbs of about the same length. The thumb is 

 much reduced. No less than eight species are found in Britain, 

 including rats, mice, and voles. The largest of these is the 

 Common or Brown Rat {Mus decumanus), which, like all 

 members of the same genus, has a long tail, and projecting- 

 tubercles on the crowns of the grinding teeth. It is supposed 



to have been intro- 

 '^ duced in the year 

 *^ ^ 1 730, and has largely- 



ousted the smaller 

 I Black Rat {M. rat- 

 tus), which is also 

 an introduced form, 

 though the date of 

 its first arrival was 

 much more remote. 

 The most familiar 

 of our mice is the 

 House- Mouse {M. 

 musculus), distin- 

 guished by the large 

 size of its delicate 

 ears. The Wood- 

 Mouse, also called 

 the Long - tailed 

 Field- Mouse {M. 

 f^jo. ~" 3 sylvaticus), is very 

 ^^ similar in appear- 

 ance, but can be 

 distinguished by its 

 white under-surface. The little Harvest-Mouse {M. minutus), the 

 nests of which are often found suspended from corn-stalks, is 

 the most diminutive of our native mammals, the smallest shrew 

 alone excepted. Voles, of which three species are native to 

 Britain (but not Ireland), are distinguished from rats and mice 

 by their clumsier proportions, shorter limbs and tail, and blunter 

 snouts. They feed entirely upon vegetable matter, their back teeth 

 being adapted to this kind of food, and having crowns of peculiar 



Fig 88 — 1 he Water Vole \Microtits aJiiphibiusj 



