CHAP. Vl] THE DENTAL SYSTEM OF THE PRIMATES 273 



It may be described as follows. Professor Bolk reminds us that 

 the South American monkeys possess a deciduous dentition in 

 which three molariform teeth occupy positions to which three 

 premolar teeth succeed as the permanent dentition is completed. 

 The permanent molars emerge behind these teeth. But the crucial 

 point in the theory consists in the suggestion that in the Old- 

 World apes and Man, two deciduous molars corresponding to the 

 first two of the Platyrrhinae appear, while the third exists but 

 is delayed in its appearance. Still it does make its way to the 

 surface ; it is called the six-year molar (in Man), and is considered 

 commonly to be the first of the " permanent " teeth to emerge. 



Furthermore, the theory of Professor Bolk postulates that 

 while the first two deciduous molars are replaced (in Platyrrhine 

 and Katarrhine Primates alike) by premolariform teeth, yet in 

 the Katarrhinae the third " deciduous " molar owns no replacing 

 tooth, the latter being suppressed. Finally it is suggested that 

 the third permanent molar tooth of the Platyrrhinae is no longer 

 present in the Katarrhinae. 



If we apply all this to the permanent dentition of the latter 

 forms (Katarrhinae), it follows that on the theory of Professor 

 Bolk, the actual conditions observed involve (a) suppression of 

 a molar tooth, viz. the last in the series of the Platyrrhinae, (b) 

 the suppression of the third premolar tooth of the Platyrrhinae, 

 and (c) delayed emergence of the third "deciduous" molar of 

 the Platyrrhinae, which loses its " deciduous " character in conse- 

 quence of the suppression postulated under (b). 



The diagrams (Fig. 199 A and B) may serve to illustrate these 

 suggestions more clearly, and although exhaustive discussion is 

 not possible in this place, the support given by Professor Bluntschli, 

 and the strong opposition of Dr Adloff demand mention. In spite 

 of that opposition I agree with Professor Bolk that his suggestion 

 makes no unreasonable demands upon the established principles 

 of Odontology. That a tooth which is ordinarily deciduous may 

 assume a permanent character is well recognized. Professor Leche 

 has recorded such an instance in certain Insectivora, and Magitot 

 states that the second (human) deciduous molar may persist while 

 the replacing tooth fails to appear. Indeed this constitutes an 

 exact repetition of the process postulated by Professor Bolk. 



D. M. 18 



