PROBLEMS OF HUMAN DENTITION 135 



It is a well-known fact that the eocene representatives of the 

 primate stem possessed three incisors in both dentitions. Dur- 

 ing the progress of primate evolution one of these was sup- 

 pressed. The genus Adapis forms a link between the primitive 

 and the recent condition, still possessing three incisors in the 

 first, but only two in the second dentition. A\'hich incisor has 

 disappeared is a much debated point, upon which authors do 

 not agree. The literature on the subject shows that each of the 

 three primitive incisor teeth has been claimed as the defaulter. 

 But I do not wish to enter into this problem, confining myself 

 to the statement, that I think it must have been the first or 

 that most mesially situated. This conviction is based upon the 

 fact that an additional incisor of conical shape not infrequently 

 occurs in man next the median plane behind the central incisor. 

 From the observations of H. B. D. Licka^ this supernumerary 

 tooth occurs, curiously enough, more frequently in Indians than 

 in Whites. This author also believes these supernumerary ele- 

 ments in the intermaxillary to be reminiscences of conditions 

 which have existed in past ages in mammals that were the ances- 

 tors of the Primates. The changes occurring in the series of 

 incisors, therefore, are of a somewhat special character. In 

 earlier times a diminution in the number of these teeth took 

 place bj^ the loss of the most mesially situated, in both jaws; 

 and in man of today the decreasing process is progressing, but 

 differs from the first phase of reduction in two regards. First, 

 it is not now the first but the second incisor, and secondly 

 the reduction is confined to the upper jaw. AVhen, in the future, 

 the loss of this second incisor has become the normal condition, 

 the singular condition will result that in a primate the construc- 

 tion of the set of teeth in the two jaws will be different, showing 

 three incisors in the lower jaw and only two in the upper. 



This progressive variation in our denture is briefly recounted 

 here, because it is one of those most generally known and there- 

 fore it should be mentioned in a discussion upon the develop- 

 mental history of our dentition. Nevertheless it is by no means 

 the most interesting. 



■' Human dentition and teeth from the evolutionary and racial stand]Kjint. 

 The Dominion Dental Journal, 1911. 



