THE TEETH OF MAMMALS. 



271 



peared utterly; thus the upper incisors of Ruminants are 

 gone, and no rudiments exist at any stage ( l ) (see page 334); 

 others still remain in a stunted and dwindled form, and do 

 not persist throughout the life-time of the animal, as for 

 instance the first premolars of a horse, or two out of the 

 four premolars of most bears. 



Before leaving this section of our subject, an instructive 

 illustration of the operation of these agencies may be given. 

 FIG. 114 ( 2 ). 



It is very easy for us to see how a "rodent" type of 

 dentition is beneficial to its possessor by rendering acces- 

 sible articles of food wholly unavailable for creatures which 



(*) Statements to the contrary have been made, and copied from book to 

 book without verification. 



( 2 ) A. Milk teeth of the Lemurine Cheiromys, with the permanent in- 

 cisors just coming into place. It differs from any Rodent by having many 

 milk teeth. i. Permanent incisor. i 2. Posterior deciduous incisor. 

 c. Deciduous canine, d, d 2. Deciduous molars. 1. Lower permanent 

 incisor. I 2. Lower deciduous canine, da, db. Lower deciduous molar. 

 B. Reduced outline figure of its permanent dentition, in which it closely 

 mimicks the true rodents. 



