VII 



DIGESTION 



77 



and when broken has the power to repair itself, but a 

 tooth does not The milk teeth are too soft and delicate 

 to do the work which the teeth must do later in life. 



The second or permanent set contains thirty-two 

 teeth when complete, but the last four, known as 

 the wisdom teeth, appear late, usually between the 

 ages of seventeen and twenty-five years. In addition 



FlG. 37. Showing permanent teeth. (From Heitzmann's " Anatomy.") 

 i, 2, incisors; 3, canine; 4, 5, bicuspids; 6, 7, 8, molars. 



to the twenty of the first set, the second has three 

 more molars on either side in each jaw, so that an 

 adult has four incisors, two canines, four premolars or 

 bicuspids, and six molars in each jaw. These are all 

 larger, stronger, and more durable than the milk teeth. 



Get from a dentist a handful of teeth. Ask him to saw one 

 crosswise and another lengthwise to show the general structure. 

 Make drawings and describe one of each class. 



