RODENTIA. 543 



and forwards. The Rodents are almost all very small animals; 

 and they are mostly very prolific. They subsist principally, if 

 not entirely, upon vegetable matters, especially the harder parts 

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

 the power of building elaborate nests, and most of them hyber- 

 nate. 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. 



The Order Rodentia comprises a very large number of fami- 

 lies, only the more important of which can be noticed here. 



Fam. i. Leporidcz. 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 



.2-2 ,0-0 3=3. W 3=3= 28 . 



I I O O 2 2 3 3 



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. Generally there is a short erect tail. 



The common Hare (Lepus timidus) is dispersed over the 

 whole of Europe, but is not met with in Sweden and Norway, 

 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. The Rabbit is also a native of temperate regions, but 

 appears to thrive, to a more than average extent, in Australia. 



Fam. 2. Cavida. As examples of this family may be taken 

 the Capybara (Hydrochcerus capybara), and the Guinea-pig 

 (Cavia aperoea). In this family the body is covered with hair, 

 without spines, and the tail is rudimentary. The Capybara is 

 the largest of living Rodents, attaining a length of three or 

 four feet. It is a South American form, leading a semi-aquatic 

 life, to which end the feet are incompletely webbed. It is a 

 harmless stupid animal, and is not unlike a small pig in ap- 

 pearance. The Cavia apercea is likewise a South American 

 animal, and is believed to be the parent stock of the Guinea- 

 pigs so often kept as domestic pets in Europe. 



Fam. 3. Hystritidcz. In this family are the well-known 

 Porcupines, distinguished from the other Rodents by the fact 

 that the body is covered with long spines mixed with bristly 



