PROBLEMS OF HUMAN DENTITION 145 



is that of a sudden disappearance of the elements. Between 

 the total absence and the normal development of the elements 

 a regular continuity of intermediate forms does not exist. And 

 it is peculiar that one looks in vain in the lower set for instances 

 of retrogression of the second premolar, as tests of the current 

 process of disappearance of this tooth from our dentition. 



In the upper set, on the contrary, the process of progression 

 is much more regular. Here we may meet with a third molar 

 reduced to a simple form. Here we may also see the second 

 incisor regressing step by step to a very simple styliform element, 

 and finally the second premolar also shows, in the upper set, 

 degrees of reduction for which we look in vain in the lower set. 

 Therefore the comparison between the two jaws, illustrates the 

 accuracy of the statement made by Bateson that the minimum 

 size of a tooth is different for different teeth. By this means 

 the evolution toward the future type of our dentition proceeds 

 in the upper jaw more slowly than in the lower. And this 

 marked characteristic enables us to show more clearly, by means 

 of intermediate forms, the direction in which this process of evo- 

 lution is moving. This is demonstrated by figures 26 and 27. 



In the foregoing pages I hope, I have demonstrated, that the 

 future upper set of teeth of the human race will differ from its 

 present construction by the loss of a, the second incisor, b, the 

 second premolar (for which will be substituted the second milk 

 molar), and c, the third molar. Now I beg to first consider 

 the denture of figure 26. It is obvious that in this upper set of 

 teeth the identical elements enumerated above are on the way 

 to regression. The second incisor, the second premolar and the 

 third molar are diminished in size equally on both sides. This 

 specimen represents a very regular intermediate form between 

 the normal dentition of the man of today and the future denti- 

 tion of the human race. Now let us examine figure 27. This 

 model, taken from a present day adult, fully represents the 

 future dentition. The second incisor is lost, the development of 

 the second premolar is suppressed and for this tooth is substi- 

 tuted the second milk molar, and finally the third molar is also 

 absent. Functionally, this dentition, I frankly admit, is not of 



