

ORDER OF RODENTS. 



583 



condyles of the lower jaw are longitudinal, not received in spe- 

 cial glenoid sockets, but gliding freely backwards and forwards 

 in longitudinal furrows. The feet are adapted for walking 

 and climbing or burrowing, the claws being well developed. 

 A peculiarity in the incisors is that they grow out as fast as 

 they are worn down ; this is due to the fact that the pulp is 

 persistent ; the enamel in front causes them to wear away 



Kg. 503.-American Flying Squirrel (Sciuropterus votoctia) 



behind so that they are chisel-shaped. The species are pro- 

 lific live mostly on vegetable food, and are of small 

 the muskrat, beaver, and capybara being the largest mem- 

 bers of the group. The flying squirrels (Fig. 503) take 

 short flights by means of the expansion of the skin between 

 * the fore and hind legs. The Norway lemmings are notice- 

 able for their remarkable migrations from the elevated 



