VERTEBRATA. 



345 



others burrow. The brain is generally smooth ; but that 

 of the Ant-eater is convoluted, and has a large corpus cal- 

 losum ; but in all the cerebellum and part of the olfac- 

 tory lobes are exposed. 



4r. Rodentia, or Gnawers, are characterized by two long, 

 curved incisors in each jaw, enameled in front, and per- 

 petually growing; they are specially formed for nibbling. 



15 



Fio. 335. Skull of a Rodent (Capybara) : 22, premaxillary ; 21, maxillary; 26, mo- 

 lar; 27, squamosal; 73, lachrymal; 15, nasal; 11, frontal; 4, occipital processes, 

 unusually developed ; i, incisors ; a, angle of lower jaw. 



Separated from them by a wide space (for canines are 

 wanting), are the flat molars, admirably fitted for grind- 

 ing. The lower jaw has longitudinal condyles, which 

 work freely backward and forward in longitudinal fur- 

 rows. Nearly all have clavicles ; and the toes are clawed. 

 The cerebrum is nearly or quite smooth, and covers but a 

 email pnrt of the cerebellum. All are vegetarian. 



FIG. 336. Incisor Teeth of the Hare. 



