266 STUDIES IN ADVANCED PHYSIOLOGY. 



the presence of the teeth for crushing the food and the 

 tongue for manipulating it during this act. 



1. THE TEETH. 



Arranged in a single row in both upper and lower jaw 

 are the teeth. These appear first as a temporary set about 

 the sixth or seventh month and disappear at about the sixth 

 or seventh year. This temporary set is usually called the 

 milk dentition for evident reasons. It is at once followed 

 by a permanent set, which consists of thirty-two individual 

 teeth, sixteen above and sixteen below. Taking half of 

 either row, the two in front are called the incisors, or cut- 

 ting teeth. They have a peculiar chisel-like edge, making 

 them specially adapted for cutting. These are followed 

 by a single canine tooth, sometimes called the eye-tooth (in 

 upper jaw) . The name canine is derived from the fact that 

 this tooth is especially developed in the carnivorous ani- 

 mals, and is there used for tearing the food. To make rl 

 more efficient as a tearing tooth in the carnivora, it is fre- 

 quently much longer than the others; in fact, sometimes so 

 long as project from the mouth. The canine is followed by 

 two premolars, called bicuspids also, from the fact that they 

 have but two fangs. The premolars are the teeth of the 

 permanent set which have replaced the molars of the milk 

 dentition. Following the two premolars we have three 

 molar teeth not represented at all in the temporary set. 

 These molars are called tricuspids also, from the fact that 

 they have three fangs. Both the premolars and the molars 

 are especially adapted for the crushing and grinding of 

 foods. The last premolar does not usually appear until from 

 the eighteenth to the twenty-fifth year, and has for this 

 reason been called the "wisdom" tooth. 



There is a marked analogy between the teeth of man and 

 those of many of the lower mammals, but modifications of 

 this typical arrangement are met with in certain classes of 

 animals. Thus, in animals like the sheep and cow, which are 

 obliged to pick the grass very closely, the upper front teeth 



