190 PHILOSOPHY OF ZOOLOGY. 



with flat nails. Tail and ears short. The eyes are con- 

 cealed under the skin. Mus typMiis. 



Grinders four on each side in both jaws. 

 (a.) Five finger;^. 



Five toes. 



68. Cheiromys. Aye-Aye. Great toe capable of act- 

 ing as a thumb, by opposing the other toes. Incisors 

 greatly compressed. Sciurus Madagascarlensis-, Gm. 



69. Bathyergus. No opposable thumb. Tail very 

 short. Eyes minute. Mus niaritimus, Gm. 



Four toes. 



70. Pedetes, Hind legs remarkably long, like the 

 Jerboa. Nails of the fingers long, those of the toes broad. 

 Mils cqfer. 



(6.) Four fingers and five toes. Incisors greatly com- 

 pressed. 



71. Pteromys. Skin expanded into a wing on the sides, 

 between the fore and hind legs, enabling the animal to sup- 

 port itself for a short time in the air. Sciurus volans. 



72. Sciurus. Squirrel. No wing. There is in youth 

 the rudiments of a fifth grinder in the upper jaw *. 



2. Summits of the grinders flat, and the enamel appear- 

 ing partially on the surface. 



The animals of this division are herbivorous. They 

 may be still farther subdivided, from the structure of their 



" It is probable that the genus Condylura of Iliger, including the Sorex 

 cristatus, ought to form a new section in this division of the Gnawers, with 

 which it is connected, by the absence of tusks. The number of incisors, 

 however, and grinders, indicates an affinity with the Ferae. According to 

 Desmarets (Journ, de Phy. ii. 89, p. 225«), it has six incisors above, and 

 four below ; fourteen grinders in the upper jaw (in all), and sixteen in the 

 lower. — Ann. Phil. xvi. p. 105. 



