COMMON THINGS MAN. 



each passing to that for whose sustenance and growth it is fitted. 

 At the age of from six to ten months, the first teeth penetrate 

 through the gum, and towards the end of the second year the 

 entire number have appeared. These twenty teeth are classified 

 according to their peculiar forms, as incisors, canines, and molars. 

 The incisors are chiselled, the canines pointed, and the molars 

 presenting a broad and rough summit. "When the mouth is 

 closed the molars of the upper jaw corresponding in position with 

 those of the lower, rest upon them. But the lower incisors and 

 canines lie within the edges of the upper ones. In each of the jaws, 

 there is, however, space for sixteen teeth, and consequently three 

 places at each side remain unoccupied. 



The relative arrangement of this set of teeth is shown in fig. 17, 

 where the incisors are indicated by I ; the canines by c, and the 

 molars by M ; the unoccupied spaces being marked " 



The first teeth which break through the jaw, are the middle 



Tig. 17. 



incisors I 1 1 1 ; these are succeeded in regular succession by the 

 lateral incisors i 2 1 2 , the canines c c, and the molars si 1 M l and 



M 2 M 2 . 



39. This first set of teeth are called the milk teeth, because of 

 their emergence from the gums at the time when the aliment of 

 the child is changed from the milk of the mother to other forms 

 of food. Towards the seventh year, these teeth begin to be 

 pushed out of the jaw by another set which have been growing 

 beneath them. The incisors and canines are pushed out by 

 another set perfectly similar in form and name, which take their 

 places. The molars are in like manner extruded by four teeth 

 in each jaw called bicuspids, having an intermediate character 

 between incisors and molars. 

 74 



