DEVELOPMENT OF MAMMALIAN TEETH. 263 



from above downwards in the upper, from below upwards 

 in the lower jaw : in both jaws vertically — are the same 

 as in the crocodile; but the process is never repeated more 

 than once in any mammiferous animal, A considerable 

 proportion of the dental series is thus changed; the 

 second or permanent teeth having a size and form as 

 suitable to the jaws of the adult as the displaced tempo- 

 rary teeth were adapted to those of the young animal. 



The permanent teeth, which assume places not previ- 

 ously occupied by deciduous ones, are always the most 

 posterior in their position, and generally the most com- 

 plex in their form. 



The term "molar," or "true molar," is restricted to 

 these teeth ; the teeth between them and the canines are 

 called "premolars;" they push out the milk-teeth that 

 precede them, and are usually of smaller size and simpler 

 form than the true molars. They are called "bicuspids" 

 in human anatomy. 



Fig. G9. 



JAWS AND TEETH OF THE LIOX. 



Thus the class mammalia, in regard to the times of 

 formation and the succession of their teeth, have been 



