THE ESSENTIAL PHENOMENA OF DIGESTION. 



31 



Behind the lips are the teeth, planted in the jaws. 

 There are thirty-two teeth in adult man, but the child 

 has only twenty, and these are called milk teeth. The 

 first dentition begins between the ages of six and 

 ten months, the middle two incisors of the lower jaw 

 usually appearing first. A few weeks later the corre- 

 sponding teeth of the upper jaw cut through, then the 



FIG. 16. 





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THE ADULT TEETH. 1, 2, the cutting teeth (incisors); 3, canine (cuspid); 

 4, 5, small grinders (bicuspids); 6, 7, 8, grinders (molars); 9, 9, neck of 

 the tooth. 



lower lateral incisors, arid afterwards the upper ones. 

 The lower canines, afterwards the upper ones, or eye- 

 teeth, are cut at the age of twelve or fourteen months. 

 Lastly appear successively eight molars, four above and 

 four below. The milk teeth begin to fall out towards 

 the seventh year, and are replaced by teeth of the second 

 dentition. Fig. 15 shows the milk teeth fully developed, 

 and the second teeth as germs. We are born with the 



