538 MAMMALS. 



lower jaw. The typical mammalian dentition already referred to may 

 be expressed as follows : — 



3-3 i-i 4-4 3-3 ii-ii 

 Incisors , canines , premolars , molars — = total 44. 



3-3 i-i 4-4 3-3 "-" 



or, using initial letters : — 



3—3 I— i 4—4 3—3 

 i. , c. , pm. , m. = 44. 



3—3 I— I 4—4 3—3 



or, recognising that the right and left side are almost invariably identical, 



and omitting the initial letters : . 



^ 3143 



We may cite the formulae for the permanent teeth of some representative 

 mammals : — 



5134 4134 3024 J014 3143 1133 



Opossum , Thylacine , Kangaroo , Wombat , Pig , Camel , 



4134 • 3134 1024 IOI4 3143 , 3123 



0033 3143 , 2033 ' 3131 ■ 3142 3142 3141 



Sheep , HoFSe , Rabbit , Cat , Dog , Bear , Seal , 



3133 3143 1023 3121 3143 3143 2141 



3133 2132 2133 2I2J 



Hedgehog , Marmoset , New World Monkey , Old World Monkey 



2123 2132 2133 2123 



2123 



Man , 



2123 



It is more interesting, however, to try to associate different kinds of 

 dentition with different kinds of diet. Thus, dolphins, which feed on 

 fish and swallow them whole, have numerous, almost uniform, sharp, 

 recurved, conical teeth, well-suited to take a firm grasp of the slippery 

 and struggling booty. To a slight extent the same piscivorous dentition 

 may be seen in seals. In the more strictly carnivorous mammals, the 

 incisors are small ; the canines are long and sharp, piercing the prey with 

 a deathful grip, while the back teeth have more or less knife-like edges 

 which sever flesh and bone. In typical insectivorous mammals the upper 

 and lower incisors meet precisely, "so as readily to secure small active 

 prey, quick to elude capture but powerless to resist when once seized," 

 while the crowns of the molars bear many sharp points. Herbivorous 

 mammals have front teeth suited for cropping the herbage or gnawing 

 parts of plants, the canines are small or absent, the molars have broad 

 grinding crowns with transverse ridges. In omnivorous mammals, the 

 incisors are suited for cutting, the canines are often formidable weapons 

 in the male sex, the molars have crowns raised into rounded tubercles. 



It is likely that the most primitive type of mammalian tooth was a 

 simple cone, such as may be seen in toothed whales. In some of the 

 extinct mammals, e.g., Triconodon, the tooth is a main cone with two 



