STRUCTURE OP THE ENAMEL IN THE PRIMATES. 599 



30. On the Structure o£ the Enamel in the Primates and 

 some other Mammals. By J. Thornton Carter, 

 Hon. Research Assistant^ University College, Uni- 

 versity of London. 



[Received May 24, 1922 : Read June 13, 1922.] 

 (Plates I. to YII. *) 



Dui-ing the past forty years the theory of the evolution of the 

 crowns of mammalian molar teeth, which is associated with the 

 names of Cope and of Osborn, has attracted the attention of a 

 large number of workers, so that a voluminous literature on the 

 subject has accumulated. 



Whilst so much work has been devoted to the gross forms of 

 the teeth, it is surprising to find that Uttle attention has been 

 given to the minute anatomy of the dental tissues as evidence in 

 throwing light on the problem of affinity. 



In the year 1850, Sir John Tomes, F.R.S., submitted to the Royal 

 Society a contribution, entitled "The Structure of the Dental 

 Tissues of the Order Rodentia " (Phil. Trans. 1850), in which he 

 gave a detailed description of the pattern of the enamel in various 

 genera, and from their comparison drew the interesting con- 

 clusion that the various families of Rodents possess a "constant 

 and exclusive character in the structure of the enamel"; further, 

 that there is a " diflerent and distinct character in each of the 

 larger groups, and that the variety of structure is constant 

 throughout members of the same group : we may take, for 

 example, the Sciuridee, the Muridse, and the Hystricidse, in each 

 of which the structure of the enamel is different and in each is 



highly distinctive" "the varieties in the structure of the 



dental tissue, with a few isolated exceptions, justify and accord 

 with the arrangements of the order into the several divisions 

 proposed by Mr. Waterhouse and deduced by him from the 

 relations of the several parts of the skull." 



Yet a year earlier than the publication of his observations on 

 the histology of the enamehin Rodents, Tomes had contributed to 

 the Philosophical Transactions a paper " On the Dental Tissues 

 in Marsupial Animals" (Phil. Trans. 1849, vol. cxxxix.), in which 

 he demonstrated a marked feature in their enamel in the form of 

 a system of tubes continuous with the dentinal tubes, this being 

 a constant character of the teeth of all Marsupials, excepting 

 only those of the Wombat. This character " attains its utmost 

 development in the Macropodidse, and is more feebly present 

 in some Dasyuridse, whilst in Myrtnecohius and yet further in 



* For explauation of the Plates, see p. 607- 



