i'I{()hjj:\is of human dentitiox 95 



i-('j)r('sontati\es of the ])riniate stem. It was never very clear 

 to iiie upon which points in their anatomical structure this 

 opinion is grounded. It is true that their nails, exce])t those on 

 the hinder thumbs, are formed like claws. But this jieculiarity 

 is a phenomenon of less value with regard to the problems of 

 phylogenetical evolution than the intlications supplied by the 

 structure of the dentition. And in comparing the anatomy 

 of the molars of the other platyrrhine monkeys — the Cebidae — 

 with those of the Hapalidae, it becomes clear that nearly all 

 Cebidae show a tendency to attain a developmental stage already 

 accomplished by the Hai:)alidae, or the total i-eduction of the 

 hindmost molar. In most genera of the New World monkeys — 

 Cebus, Ateles, Chrysothrix, Pithecia, Nyctipithecus — the third 

 molar is already reduced in a \'ery large degree, ha\'ing only a 

 single root and a very small crown without cusp-differentiation. 

 Usually this hindmost tooth of the Cebidae is a far more reduced 

 element of the dentition than the third molar in man. The fact 

 that the Cei:)idae apjiroach a structure of their dentition already 

 acquired by the Hai^alidae, is to me a sufhcient ground to place 

 the latter on a higher level of phylogenetical evolution than the 

 former. It is worthy of mention, that the investigation of 

 Weber showed the brain of the ]\Iarmoset, although a lissen- 

 cephalous one, to be relatively heavier than even that of man. 



Therefore, I consider the dentition of the Hapalidae an inter- 

 mediate form between that of Cebidae and catarrhine Primates, 

 notwithstanding the reduced number of their molars. The loss 

 of the hindmost molar, w^as the first step w^hich led the plat- 

 yrrhine ancestor of man to the more progressive dental struc- 

 ture peculiar to all Old World Primates. We will return later 

 on to the cause of this reduction. 



The i^rimitive number of three molars was regainetl in conse- 

 (juence of the third milk molar becoming permanent and of the 

 suppression of the develoi^ment of the third premolar. This is, 

 I admit, somewhat unusual in the evolution of dentition. But 

 there are other examples, well-known to us, in which the same 

 phenomenon took ]:)lace, and in consequence of which the func- 

 tional set of teeth became a mixed one, composetl partial!}' of 



