84 



THE PERMANENT INCISORS 



wearing down, and the distance apart becomes more and 

 more apparent. 



From the fifth to the eighth month the inner teeth 

 will usually appear as in Fig. 19 ; and at ten months 

 this change shows more clearly, as in Fig. 20, and the 

 spaces between them begin to show very plainly, till 

 at a year old they ordinarily present the appearance 

 of Fig. 21 ; and at the age of fifteen months that shown 

 in Fis:. 22, where the corner teeth are not more than 

 half the original size, and the centre ones still smaller. 



The permanent teeth are now rapidly growing, and 

 preparing to take the place of the milk-teeth, which 

 are gradually absorbed till they disappear, or are pushed 

 out to give place to the two permanent central incisors, 

 which, at a year and a half, will generally present the 

 appearance indicated in Fig. 23, which shows the inter- 

 nal structure of the lower jaw at this time, with the 

 cells of the teeth, the two central ones protruding into 

 the mouth, the two next pushing up, but not quite 



Fig. 23. Eighteen months. 



Fig. 24. Two years past 



grown to the surface, with the third pair just percep- 

 tible. These changes require time ; and at two years 

 past the jaw will usually appear as in Fig. 24, where 



