138 PROF. DR. L. BOLK 



logical appearance, caused by some irregular arrangement of 

 the teeth, or by some obstacle in the normal substitution of the 

 milk tooth; for if such were the case, the second milk molar of 

 figure 22 surely would have dropped out, as, owing to the gap 

 immediatelj^ back of it, it is in a very unfavorable position to 

 maintain itself. 



In carefully examining all specimens of persisting m^, present 

 in my collection, I was not able to find a single instance in which 

 the dental arch was an irregular one. In all cases the persisting 

 milk molar participates in the structure of the arch as a perfectly 

 normal element. One of my preparations is represented in figure 

 23. I chose this specimen because it is the mandible of a fairly 

 old man, as is shown by the much worn occlusal surfaces of the 

 incisors and molars. 



As a last general remark I will draw attention to the fact that 

 a persisting m2 appears more frequently on the right than on the 

 left side. This fact is not in accordance with the rule that in 

 the left half of the human body anomalies seem to be more 

 abundant than in the right one. So far as known to me this 

 curious fact is as yet unexplained. 



After these general observations regarding the persisting second 

 milk molar, we enter into the ])roblem of its significance from an 

 evolutionary standpoint. I recall that stress has been laid upon 

 the fact, that this anomaly is not at all of a pathological char- 

 acter, but that it must be regarded as a normal symptom of the 

 future development of our denture. It is a variation of a pro- 

 gressive nature. Furthermore, emphasis has been placed upon 

 the fact that this behavior of the second milk molar must be 

 considered, together with the reduction of our third molar, from 

 a connnon point of view. 



The relation between the two variations is, I believe, a very 

 simple one. The third molar of man is an element progressing 

 toward reduction. It may be taken for granted that the human 

 race will eventually be different from all other Primates by the 

 complete loss of this component of the denture. But in conse- 

 quence of this I'eduction the grinding surface is shortened; and 

 it seems to me that at the anterior end of the molar region the 



