PROBLEMS OF HUMAN DENTITION 93 



tition of the Platyrrhinae and the Catarrhinae is wholly differ- 

 ent. But there is one point connnon to both hypotheses worthy 

 of special reference because it constitutes a weak side of each 

 of the hypotheses. 



The dental formula of the platyrrhine monkeys (save the 

 Hapalidae) runs as follows: 



ii. u. c. nil. nio. nis. 



Ii. I.. C. Pi. P.. Ps. M,. ^I.. M3. 



and that of the catarrhine Primates: 



ii. io. c. nil. nio. 



Ii. Io. C. Pi r.2. Ml. Mo. M3. 



In these formulas the elements of the milk dentition are written 

 in small print and those of the permanent set of teeth in capital 

 letters. The formulas as above written are not intended to give 

 expression to any homology between the teeth of the two groups 

 of primates. In accepting either of the hypotheses mentioned 

 abo\-e one must keep in view the fact that the catarrhine denti- 

 tion not only arose from the reduction and final loss of a premolar 

 in the permanent set of teeth, but also of its predecessor in the 

 milk dentition. It seems to me to be very important that in 

 none of the recent genera of the New World monkeys is a reduc- 

 tion of a tooth to be seen either of the first or third milk molar, 

 or of the first or third .premolar. It is altogether probable that 

 in the extinct ancestors of the catarrhine Primates such a reduc- 

 tion really took place. But one looks in vain both in the upper 

 and lower jaw of this group of Primates for any proof that a 

 tooth in the premolar region has been lost. In its whole extent 

 this portion of the dental arch is always regularly constructed, the 

 teeth standing very closely apjiroximated. Furthermore in catar- 

 rhine monkeys a diastema, especially between the canine and first 

 premolar is wanting. These facts surely are not very favorable 

 to the opinion that the reduction in the number of the premolars 

 in Primates happened in the common way — in consequence of the 

 loss of a premolar and its predecessor in the milk dentition. 

 For, in case such a process really happened, the situation of the 

 lost tooth would be indicated bv a diastema. The objection to 



