RODENTIA. 545 



the Muridce, comprising the Rats, Mice, and Lemmings. In 

 this family the tail is long, always thinly haired, sometimes 

 naked and scaly. The lower incisors are narrow and pointed, 

 and there are complete clavicles. The hind-feet are furnished 

 with five toes, the fore-feet with four, together with a rudi- 

 mentary pollex. 



The Rats (Mus rattus and Mus decumanus\ the common 

 Mouse (Mus muscttlus), the Field-mouse (Mus sylvaticus\ and 

 the Harvest-mouse (Mus messorius\ are all well-known British 

 examples of this family, and are too familiar to require any 

 description. 



A less familiar example of this family is the Lemming (Myodes 

 lemmus). This curious little Rodent is found inhabiting the 

 mountainous regions of Norway and Sweden. It is chiefly re- 

 markable for migrating at certain periods, generally towards the 

 approach of winter, in immense multitudes and in a straight 

 line, apparently in obedience to some blind mechanical im- 

 pulse. In these journeys the Lemmings march in parallel 

 columns, and nothing will induce them to deviate from the 

 straight line of march. 



Fam. 6. Dipodidce. The sixth family of the Rodents, which 

 is sufficiently important to need notice, is that of the Dipodida 

 or Jerboas, mainly characterised by the disproportionate length 

 of the hind-limbs as compared with the fore-limbs. The tail 

 also is long and hairy, and there are complete clavicles. The 

 Jerboas live in troops, and owing to the great length of the 

 hind-legs, they can leap with great activity and to great dis- 

 tances. They are all of small size, and inhabit Russia, North 

 Africa, and North America. 



Fam. 7. My oxides. The members of this family are com- 

 monly known as Dormice, and they are often included in the 

 following family of the Squirrels and Marmots. They only re- 

 quire to be mentioned, as they must not be confounded with 

 the true Mice (Muridce) on the one hand, or the Shrew-mice 

 (SoricidcR) on the other ; the latter, indeed, belonging to an- 

 other order (Insectivord). The common Dormouse (Myoxus 

 avellanarius) is a British species, and must be familiarly known 

 to almost everybody. 



Fam. 8. Sciuridcz. This is the last family of Rodents which 

 calls for any special mention, and it comprises the true Squir- 

 rels, the Flying Squirrels, and the Marmots. 



The true Squirrels (Sciurus) are familiarly known in the 

 person of our own common species (Sciurus vulgaris). Numer- 

 ous species more or less closely allied to our Squirrel occur in 



VOL. II. 2 M 



