PHOBLEMS OF HIMAX DEXTITIOX 139 



denture stri\'os to ronipeiisate for the loss at the posterior end, 

 for the oTinding surface of the second milk molar is a larger one 

 than that of the thii-d i)reniolar. 



In thus interpreting these phenomena, there appears a very 

 remarkable continuity in the developmental history of the pri- 

 mate dentition; for, in the first section of this conununica- 

 tion, it is demonstrated that the dentition of the catarrhine 

 Primates — including man — evolved from a platyrrhine mon- 

 key's dentition by the reduction of the hindmost molar, and the 

 permanency of the third milk molar. And we now see that the 

 dental variations, when considered in relation to each other, 

 furnish a clear indication that an identical process is taking 

 place in man today. This concordance leads to the conclusion 

 that the future luunan race will differ from the present with 

 regartl to its dentition, in the same manner in which the 

 catarrhine monkeys once differed from the platyrrhine. 



This conclusion may be expressed in a clear manner, by the 

 following series of dental formulas. In the first the dental 

 formula of one of the ( 'ebidae is written, in the second that of 

 one of the Hapalidae, in the third the complete normal dental 

 formula of man in its actual state, in the fourth the formula is 

 given of a human dentition in which the third molar is reduced, 

 and is indicated as a first distomolar, while the original first 

 distomolar becomes the second; and in the fifth formula the 

 final stage of the developmental history of human dentition is 

 represented. In this formula the second incisor is also indi- 

 cated as a lost element. In all these schemes the regressed 

 teeth are placed in brackets, while the milk teeth are indicated 

 in small print. 



I C'ebidae 



II Hapalidae 



ii lo c nil nio m, 



Ii I2 C Pi P, P3 M, ^L ^U 



ii lo c nil nio ni3 



Ii I, C Pi Po P3 .All AIo [Di] 



THE AMERICAN- JOURNAL OF AXATOMY, VOL. 19, NO. 1 



