606 MR. J. THORNTON CARTER ON THE 



The microstructure of the enamel, howevei-, appears to be par- 

 ticularly constant. In the long and well-authenticated series of 

 creatures comprising the ancestiyof the Horses, the microstructure 

 of the enamel does not change, in spite of the modification of the 

 teeth from the brachydont form in Eohipjjus through all the pro- 

 gressive stages leading up to the complex hypsodont molar teeth 

 of recent horses. 



In the Marsupials the pattern of the enamel in recent and 

 fossil Australian forms appears to be identical with that of the 

 teeth of Peradectes from the Tiffany beds of Colorado (Lower 

 Eocene). 



Certain fossil rodents from the Eocene exhibit a close 

 similarity in enamel structure to recent forms, and where, as in 

 Chiromys, a Lemur has evolved a rodent dentition, the structure 

 of its enamel still retains its Lemurine character. 



It was my intention to hold over a description of the minute 

 structure of the teeth of Primates until I had published an 

 account of the structure of the teeth in Insectivores, recent and 

 fossil, and of the primitive Creodonts, the material for which has 

 been examined, together with that of a large number of other 

 Eocene mammals. But Professor J. P. Hill, F.R.S., and Professor 

 D. M. S. Watson, F.R.S., were of the opinion that the facts 

 presented in this communication would be of immediate interest 

 to the Fellows of the Society, the more so as recent palseonto- 

 logical discoveries have provided fresh evidence of the antiquity 

 of the Higher Primates, 



In conclusion, I have to express my deep gratitude to my 

 colleague, Major G, S. Sansom, and to Mr. F. J. Pittock for 

 their kindness in preparing the micro-photographs used in the 

 illustrations, and to Professoi's Hill and Watson for constant 

 encouragement. 



Above all I have to thank Dr. W. D. Matthew, F.R.S., for 

 providing invaluable material, and for most A^aluable information 

 and suggestion in conversation during his recent visit to Europe. 



Most of the recent material employed was acquired by pur- 

 chase, but I am deeply indebted to the Zoological Society through 

 Mr. R. I. Pocock, F.E..S., for the gift of teeth of Ghiromys, 

 and to Professor J. Elliot Smith, F.R.S., for a mandible of 

 Tarsius. 



Summary. 



A microscopical examination of the teeth of Primates discloses 

 the fact that all members of the suborder Lemuroidea possess, in 

 a vai-ying extent, the character of a penetration of tubes into the 

 enamel. 



In the Lemurinse this penetration is slight, but in the Indrisinse 

 it is very rich. 



The Galagos and Pottos also have a rich penetration, but in 

 Nycticehus it is but feeble. 



