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. 



4. 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. 



Fio. 335. Skull of a Rodent (Capybara) : 22, premaxlllary ; 21, maxillary ; 20, mo- 

 lar ; 27, sqnaniosal ; 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 

 small part of the cerebellum. All are vegetarian. 



"W 



FIG. 336. Incisor Teeth of the Hare. 



