226 GNAWING QUADRUPEDS. 



plates of enamel, to correspond with this motion. 

 But although these teeth are generally flat with 

 linear plates of enamel, they are sometimes marked 

 with blunt tubercles, and more rarely with sharp 

 points. In the first case the animals are strictly 

 frugivorous, in the last occasionally carnivorous, 

 and in the other omnivorous. The stomach is 

 simple, the intestine very long, the ccecum of great 

 size, often exceeding that of the stomach. These ani- 

 mals are 'generally extremely active and lively, and in 

 all of them the posterior extremities are proportionally 

 more developed than the anterior, so that they ad- 

 vance by a series of leaps, rather than by walking 

 or running. Such of them as are furnished with 

 perfect clavicles, are capable of raising objects be- 

 tween their fore feet, and often of climbing upon 

 trees. The Rodentia may be divided into several 

 families : The Sciuridse, or Squirrels ; Muridas, or 

 Rats and Mice ; Castoridae, or Beavers and allied 

 genera ; Leporidae, or Hares ; and several others, 

 which it is unnecessary to enumerate, as they have 

 no representatives among our indigenous quadru- 

 peds. The British species, fourteen in number, be- 

 long to five genera : 



I. SCIURUS. SQUIRREL. Perfect clavicles ; grinders 

 simple, that is, composed of enamel and ivory only, 

 five above, and four below on each side, their sum- 

 mits tubercular ; upper incisors chisel-shaped, lower 

 pointed ; tail long, bushy, with the hairs directed 

 laterally. 



