54 COMPARATIVE DENTAL ANATOMY 



by flattening of its base, to cut substances; the 

 canine is a single cone elongated and sharpened, 

 to seize and tear flesh; the premolars (bicuspids), 

 as in man, are formed by the addition of a second 

 lingual cone to the primitive buccal cone, to crush 

 food, or by the addition of a third cone to form 

 the tritubercular molar, or of the fourth to form 

 the quadritubercular molar, etc., to grind food. 

 There is sometimes special development of special 

 teeth for secondary purposes, as of the incisors 

 of the Elephant, Sirenia, Narwhal; or the canines 

 of the Walrus, the extinct carnivora, the wild 

 boar; or of the blades of the premolars of the 

 carnivora. The premolar and molar teeth were 

 evidently developed by the duplication of cones 

 by fusion or addition, which are traceable back 

 along the paths of their development through 

 geologic ages, to simple conic reptilian forms. 

 There was first the simple cone alternating with 

 that of the opposite jaw, as in the living reptiles 

 (Haplodont form) ; then the double cone, formed 

 by the addition of a second cone (as the premolars 

 of man) ; then the third cone was added to form 

 the triconodont type, which was modified to the 

 tritubercular form of molar (the primitive type 

 of all molars) ; then the projecting heel or cingule 

 (talon) led to the formation of the fourth tubercle 

 (the quadritubercular molar) ; then the addition 

 of the fifth and other tubercles formed the addi- 



