ITS ANCESTORS AND RELATIONS. 23 



sions. The hemispheres of the cerebrum are espe- 

 cially small, compared with the cerebellum aud ol- 

 factory lobes. This is exactly iu accord with what is 

 now generally known of the progressive diminution 

 of the size of the brain in all groups of animals the 

 further back we pass from the present time. 



The teeth were of the same number as in the 

 great majority of Eocene mammals — namely, three 

 incisor or front teeth, one canine or corner tooth, 

 and seven cheek teeth, consisting of four premolars 

 and three molars,* or eleven altogether on each side 

 of the upper, and the same number in the lower, jaw, 

 making a total of forty-four. These numbers are 

 briefly expressed in the formula 



. 3 1 4 3 11 _ AA 

 i-^c, jil»4> w 3 = jj x 2 = 44. 



This is an extremely important formula to. remem- 

 ber, as it is, as just mentioned, the one most com- 

 monly met with in mammals of the early Tertiary 

 periods, and therefore the most generalized condition 

 of dentition among all the higher orders of the class, 

 and the one from which, by suppression or loss of 

 certain of the teeth, all the special modifications now 



* The back teeth, grinding teeth, or cheek teeth are di- 

 vided into premolars and molars or true molars. In the ungu- 

 lates there are three or four of the former and always three 

 of the latter, which are the hindermost of the series and not 

 preceded by milk teeth. 

 3 



