( 788 ) 



rhines it still belongs to the milk teeth. May this not be the 

 explanation of the fact that our first molar still breaks through 

 in connection with the teeth of the set of milk teeth, and still 

 before the appearance of the first replacing tooth, while the 

 second tooth appears only after a period of some years ? By this 

 early appearance of our first molar it functionates indeed for 

 some time together with the complete set of milk teeth and so 

 according to my opinion the set of teeth of man still possesses in 

 this period a composition as in the first lifetime of the Platyrrhines. 

 Still more distinctly than from the time of the eruption this relation 

 appears wlien the first forming during the ontogonese is more closely 

 investigated. I derive the following about this from the wellknown 

 investigation of Rose '). Between the 9^'' and J 2''' week ofthefaetal 

 development the papillae of the milk teeth are invaginated in the 

 dental band (Zahnleiste) which grows on uninterruptedly towards the 

 back, and already in the l?'^'^ week of the development the papilla 

 of the first molar is invaginated. So with man there is not the least 

 histogenetical discontinuity between the forming of the milk teeth 

 and of the first molar. C>nly after the course of a year, so 

 four months after the birth the dental band begins to grow on 

 towards the back and not before the 6"' month after birth the 

 papilla of the second tooth is invaginated. So while M^ is formed 

 immediately after m^ with man, a pause of about a year begins 

 after this first development. So both from morphology and ontogeny 

 arguments may be derived for the hypothesis that m^ of the Platyr- 

 rhines is homological to M^^ of the Catarrhines. 



My hypothesis however still contains another clement viz. the 

 reduction of P^ and M^ of the Platyrrhines. 



Let us first consider the reduction of M^. From my above men- 

 tioned deduction of the catarrhine set of teeth given in a formula, 

 follows that I come in conflict with a rather generally accepted 

 opinion that the three molars of the Catai'rhines should be homo- 

 logue to the three molars of the Platyrrhines. According to my 

 opinion M^ of the Platyrrhines is homologue to il/, of the Catarrhines, 

 Mi of those homologue to M^ of these, and in the set of teeth of the 

 Catarrhines the honiologon of M^ of the Platyrrhines is wanting. 

 If this tooth should also appear by the last mentioned group 

 of Primates it would become a M\. Now it is a fact that is 

 universally known that a more or less developed fourth molar 

 is not seldom with man and among the Anthropoids, especially 



1) G. Rose, Ueber die Entwicklung der Ziiline des Menschen. Arch. f. mikrosk. 

 Anat. End. XXXVIII. 



