164 EODENTIA. 



and a gall-bladder generally present, but deficient in some rats ; and the 

 pancreas is also large. The brain is small, either tapering in front as 

 in birds, or somewhat circular and smooth, and without convolutions. The 

 cerebellum is scarcely overlapped by the cerebrum. 



There is no scrotum in most of the rodentia, but the testes increase 

 much in size in the breeding season, and at that time pass into a sort of 

 temporary scrotum. Most possess a bone in the corpus cavemosum of 

 the penis. The uterus has two horns, and in some indeed is actually 

 double. 



The rodents are mostly animals of small size, the Capybara, the Porcu- 

 pines, and the Beavers, being the giants of the order. Their eyes are 

 directed sideways. The opening of the mouth is small, and many have 

 cheek-pouches. The ears are moderate or large. Their hmbs are usually 

 short, the hind extremity in many much larger than the anterior. They 

 Bxe usually clad with hair, in a few with bristles or spines. The tail varies 

 much in size, is sometimes hairy, at others naked or scaly. They live 

 chiefly on vegetable substances, often on hard nuts, roots, the bark of 

 trees, &c. ; and many are nocturnal in their habits. Many of them build 

 artificial nests, and a few manifest a constructive instinct in association ; 

 whilst others are remarkable for their migrations. They are very prolific, 

 often producing several litters in the year, and the young quickly attaining 

 maturity. Many hybemate like reptiles. In many of their anatomical 

 features, as well as in their habits, we are reminded of birds, and they 

 manifest a decided inferiority of type. Cheiromys, a Lemurian form 

 already alluded to, is the only animal that possesses teeth similar to the 

 rodents, with which it was classed by some. Blyth considers that " per- 

 haps the nearest aflSnity of the Bodentia, is with the Elephant among 

 the Pachydennata."* 



The division of the rodents into groups is attended with some 

 difficulties, and various classifications have been proposed. I shall here 

 group the Indian rodents in four families — Sciuridee, squirrells ; Muridce, 

 rats ; Hyatriddce, porcupines ; and Leporidce, hares ; which, indeed, are 

 considered by some to embrace the whole of the order ; to which has 

 recently been added the Saccomyidee, or pouched rats, ■\ whilst many 

 systematists malce separate families of the dormice, Myoondw ; jerboas, 

 Dipodidce ; voles, Arvioolidce ; mole-rats, Aspalacidee and Bathyergidm ; 



•Cuvier's Animal Kingdom. Transl. p. 109. t Ki'rfe Sclater, Qiiaiterly Jour. Science, October 1865, 

 p. 617. 



