YERTEBRATA. 
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. 
15 n 
Fig. 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 
small part of the cerebellum. All are vegetarian. 
Fig. 336.—Incisor Teeth of the Ilare. 
