62 COMPARATIVE DENTAL ANATOMY 



and size, but still retain suggestions of the fea- 

 tures of these teeth in the Carnivora. 



The Tubercular and grinding teeth. The very 

 lowest form in which grinding organs appear are 

 the cusped prominences on the triturating plates 

 of the Crustacea and some insects, but these are 

 not true teeth. They are, however, analogous to 

 true grinding teeth, as they are employed for the 

 same purpose. Very few of the Invertebrates 

 possess triturating apparatus of any sort. In the 

 Vertebrates, crushing teeth appear in some forms 

 of fishes, which have well-developed pavement 

 teeth of various forms for crushing the shells of 

 mollusks and crustaceans. These are not true 

 molars, however, as they do not triturate food nor 

 insalivate it. Tuberculate teeth proper do not 

 appear until in the higher forms of reptiles, as 

 some of the lizards have teeth, which are slightly 

 tubercular, and these are the beginnings and fore- 

 runners of the molar series in the Mammalia. 

 The lizards show the first tendency to the dupli- 

 cation of cusps, which are repeated over and over 

 in various directions in the Mammalia. In the 

 Mammalia the molar series of the permanent 

 teeth is divided into two sections, — (a) the pre- 

 molar (or succedaneous teeth), and (b) the true 

 molars, which have no deciduous predecessors. 

 The grinding teeth of the deciduous set are 

 molars. The premolars are the small grinders 



