DIGESTION 



175 



ning of the third year. The order of their eruption, the periods, on 

 the average, at which they come into view, is as follows : The lower cen- 

 tral incisors appear at seven months, and the upper central incisors a 

 little afterward; the upper lateral incisors show at nine months, and the 

 lower lateral incisors somewhat later; the first molars in both jaws about 

 the twelfth month; the canines at about the eighteenth month; and the 

 second (that is, the posterior) molars at about the twenty-fourth 

 month. The temporary teeth are similar in general shape to the 

 permanent teeth, but are much smaller, bluer in tinge, and less firmly 

 implanted. 



The permanent set of teeth begin to displace the temporary teeth during 

 the sixth or seventh year, although the sacs of all the permanent teeth, as 

 well as those of the temporary set, are present in the jaw at birth. At the 



FIG. 82 



Upper or 

 lower jaw 



Incisors 





Molars 



Bicuspids 



-4 Canine 



The permanent teeth. 



The numbers denote the respective times of their eruption in years. 

 (Hall.) 



sixth year, therefore, the jaw contains forty-eight teeth the whole of 

 the deciduous set and all the permanent teeth except the third molars 

 (" wisdom teeth"). The twenty teeth of the temporary set are replaced 

 by a like number of somewhat similar permanent teeth, and these have 

 similar names save that those replacing the temporary molar teeth are 

 called bicuspids and have each two cusps instead of the molar's three. 

 In addition three molars are added posteriorly on each side of each jaw, 

 making the permanent teeth thirty-two in number. The first of the true 

 molars (that is, that nearest the middle line), the earliest of the permanent 

 teeth, appears at about the end of the sixth year, then the central incisors 

 at seven years, the lateral incisors at eight years, the first bicuspids at 

 nine years, the second bicuspids at ten years, the first canines at eleven 

 years, the second canines at twelve years, the second molars between the 

 twelfth and thirteenth years, and the unreliable third molars, or wisdom 



