CHAP. Vl] THE DENTAL SYSTEM OF THE PRIMATES 271 



While the human formula is tending (as described above) to 

 become 



(/) I I C{ Pmf M|. 



The comparison of the normal human formula (e) with the 

 primitive formula (a) will shew that in human evolution a net 

 loss amounting to two incisor, two premolar and five molar teeth 

 has been experienced. With the exception of the canine teeth, 

 each type (incisor, premolar, and molar) has been reduced in 

 number, though the degree of reduction varies. In the attempt 

 to trace the history of the reduced dentitions, the problems as to 

 the particular teeth that are missing from each region have 

 attracted much attention, though final conclusions have not been 

 reached on several points. Thus in regard to the incisors, the 

 literature of the subject shews that each of the three primitive 

 incisor teeth, cf. formula (6), has been claimed as the defaulter. 

 Even in the critical account furnished by Bluntschli in 1910 1 , the 

 question seems to be left an open one. 



As regards I\ (the median incisor tooth), it may be remarked 

 that the wide interspace in the Lemurine dentition between the 

 upper median incisor teeth is suggestive, and that a super- 

 numerary incisor tooth is not infrequent in this situation. Gadow 

 adopts this view (as, I believe, does Lydekker also) ; Elliot Smith has 

 recently recorded, while the present writer has observed, instances 

 of a supernumerary incisor tooth in the position indicated. 



The view that I 2 is the missing tooth is supported by Turner, 

 Albrecht, and Wilson and is based largely upon considerations of 

 the arrangement of the incisor teeth in cases of persistence of the 

 suture dividing the premaxilla and maxilla (hare-lip)-. 



Windle (J. A. and P., Vol. XXI., pp. 84, et seq.) favours the view 

 that I 3 has been suppressed ; this view rests on the fact that the 

 pre-canine space is a common locality for the occurrence of super- 

 numerary teeth ; while if it be granted that the characters of the 

 teeth merge by insensible gradations into one another, the space 



1 Vierter Jahrschrift der Naturforschenden Gesellschaft in Zurich, Jahrgang 

 55/56, 1910, 1911. 



2 For expositions of this subject cf. Windle, J. A. and P., Vol. xxi., and 

 Tomes, Dental Anatomy. 



