8 Early History and Habits 



changes which take place up to the age of three years 

 depend only on the fore-teeth being worn away more or 

 less, and the black hollows being obliterated gradually 

 by contact with food. In thirteen to sixteen months the 

 cavities on the surface of the pincers are effaced ; they 

 are then said to be razed. In sixteen to twenty months 

 the intermediate fore-teeth are likewise razed, and in 

 twenty to twenty-four months the same thing takes place 

 with the corner teeth. 



Fig. 2.— At eighteen days. Fig. 3. — At three years. 



The second dentition commences at the age of two 

 and a half or three years (Fig. 3). The milk-teeth may 

 be recognized by their shortness, their whiteness, and the 

 construction round their base, called the neck of the tooth. 

 The teeth which replace them have no neck, and are much 

 larger. The pincers are the first to fall out and be replaced 

 by new ones. At the age of from three years and a half 

 to four years the intermediate fore-teeth experience the 

 same change, and the lower tushes begin to make their 

 appearance. The corner teeth are also renewed when be- 

 tween four and a half to five years ; the upper tushes like- 

 wise pierce the gums, and about the same date the sixth 

 grinder shows itself. 



A depression, or small hollow, may be noticed on the 

 surface of the crown of the second growth of fore-teeth, 

 just as in the milk-teeth, and these hollows are gradually 

 worn away in the same fashion, 



