92 PROF. DR. L. BOLK 



accepted scheme. The embryological development of mam- 

 malian teeth is a process more complicated than the description 

 of it as given in text-books of anatomy or odontology would 

 lead one to suppose. 



First I shall treat of the manner in which the dentition of man 

 (and of all other platyrrhine Primates) is a development of the 

 more primitive form of platyrrhine dentition. Then the prob- 

 lem will be discussed as to which set of teeth our molars belong 

 (to the first or milk dentition, or to the second or permanent set 

 of teeth) ; and finally I shall give my conception as to the future 

 changes which will occur in human dentition. 



FIRST PROBLEM: THE RELATION BETWEEN THE DENTITION OF 

 PLATYRRHINE AND CATARRHINE PRIMATES 



As is generally known, one of the most striking anatomical 

 differences between the two groups of Primates (the Platyrrhinae 

 and the C'atarrhinae) is that the monkeys of the New World 

 possess three premolars and three milk molars in each jaw, 

 whereas in catarrhine monkeys and likewise in man, there are 

 only two of each of these teeth. There is some difference be- 

 tween the two families of American monkeys, the Hapalidae 

 possessing two molars only, whereas in the Cebidae there are three 

 of these teeth, as in all other Primates. Therefore the majority 

 of New World monkeys have a set of teeth whose post-canine 

 portion possesses one tooth more than the corresponding portion 

 of the Old World monkeys, or of man. 



It is a common view of anatomists and zoologists that the 

 dentition of the latter evolved from that of the former group by 

 the loss of one of the premolars. But there is no agreement as to 

 the premolar which was reduced. Most investigators maintain 

 that the first premolar of the platyrrhine monkeys is wanting in 

 the catarrhine group. Therefore the first premolar of the latter 

 should be considered the homologue of the second premolar of 

 the former. Other investigators, on the contrary, assert that it 

 is the third premolar of the Platyrrhinae which is wanting in the 

 other families of the Primates. I do not agree with either of 

 these views. My opinion as to the relation between the den- 



