THE TEETH OF VEETEBEATES 57 



parts of the jaw as to the forms of the teeth, but 

 only as to size, and there is not sufficient differ- 

 entiation to admit of classification. But one 

 function is performed in these low classes, that 

 of prehension, for mastication is not yet devel- 

 oped. In the higher Vertebrates, the Mammalia, 

 however, the teeth are more differentiated and 

 special forms are evolved for special uses. Thus 

 the teeth situated in the front of the oral cavity, 

 from their form, are called incisors, or cutters, 

 and their function is to cut or divide food. The 

 large conical teeth situated immediately distally 

 of the incisors are called the canines (from being 

 extra well developed in the dog and other carniv- 

 orous animals), and are used for seizing and tear- 

 ing flesh. The next teeth are the molars, the 

 crushers and grinders, which perform the func- 

 tion of mastication and insalivation. These are 

 divided into two classes, the premolars and true 

 molars. The premolars are the permanent teeth 

 just distally of the canines which succeed the de- 

 ciduous molars. These are called the bicuspids 

 in man. After these are the full or true molars, 

 which are the true grinding teeth. Thus the per- 

 manent teeth of mammals are classified into four 

 groups, — (1) the Incisors, (2) the Canines, (3) 

 the Premolars, (4) the Molars. With this ar- 

 rangement it is convenient to express in a mathe- 

 matical scheme the number of the teeth of any 



