1 64 RODENTIA. 



liver is large, 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 con- 

 volutions. 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 cavernosum 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 limbs are usually 

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

 are 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 hybernate 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 " perhaps the nearest affinity of the 

 Rodentia is with the Elephant among the Pachydermata" * 



The division of the rodents into groups is attended with some diffi" 

 culties, and various classi6 cations have been proposed. I shall here 

 group the Indian rodents in four families Sciuridce, squirrels ; Muridce, 

 rats ; Hystricidce, porcupines j and Leporidce, hares ; which, indeed, are 

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

 recently been added the Saccomyidce, or pouched rats,f whilst many 

 systematists make separate families of the dormice, Myoxidce ; jerboas, 

 Dipodidce ; voles, Arvicolidce ; mole-rats, Aspalacidce and Bathyergidaz; 



* Cuvier's Animal Kingdom (Transl.), p. 109. 



f Vide Sclater, Quarterly Jour. Science, October, 1865, p. 617. 



