754 MANUAL OF ZOOLOGY. 



plants, such as the bark and roots. Many of them possess the 

 power of building elaborate nests, and most of them hibernate. 

 They are very generally distributed over the whole world, but 

 no member of the order has hitherto been detected in rocks 

 older than the Eocene Tertiary. 



In accordance with the number of the incisor teeth, the 

 Rodents may be divided into the following two primary 

 sections : 



(i.) SIMPLICIDENTATA. Only two upper incisors, and these 

 enamelled in front only. This division comprises all the 

 Rodents except the Leporidce and Lagomydce. 



(2.) DUPLICIDENTATA. (Hares, Rabbits, and Calling 

 Hares). Two rudimentary incisors behind the large central ones. 



The order Rodentia comprises a very large number of fami- 

 lies, which can be merely noticed here. 



Fam. i. Leporida. In this family are the Hares (Lepus 

 timidus) and Rabbits (Lepus cuniculus), distinguished amongst 

 the Rodents by the possession of two small incisors in the 

 upper jaw, placed behind the central chisel-shaped incisors, so 

 that there are four upper incisors in all. The molars and prae- 

 molars are rootless, and the dental formula is 



z 2 ^ 2 ; ,HL; /3n3 m 3=3 = a8> 

 i i oo 22 33 



The clavicles are imperfect. The fore-legs are furnished 

 with five toes, and are considerably shorter than the hind-legs, 

 which have only four toes. The two orbits communicate by 

 an aperture in the septum. There is a short erect tail. 



The common Hare (Lepus timidus) is dispersed over the 

 whole of Europe, but is not met with in Northern Scandinavia, 

 its place there being taken by the Mountain-hare (white in 

 winter), which occurs commonly in Scotland. As a rule, the 

 Hares occur in temperate regions, but some are found in 

 Africa, and one species (Lepus glacialis) is a native of the Arctic 

 regions, whilst the common American Hare (L. Americanus) 

 extends from Canada to Mexico. The Rabbit (Lepus cunicu- 

 lus) is also a native of temperate regions, but appears to thrive, 

 to a more than average extent, in Australia. 



Fam. 2. LagomydcE. In the Calling Hares or Pikas (Lago- 

 mys\ which form this family, the legs do not differ much in 

 size, there is no visible tail, and the clavicles are nearly com- 

 plete. There are only five back teeth (instead of six) on each 

 side of the upper jaw, but there are two rudimentary incisors 

 besides the central ones. They resemble the Guinea-pigs in 

 form, and are found in Russia, Siberia, and North America. 



