STRUCTURE OF THE ENAMEL IN THE PRIMATES. 601 



Included in the material supplied by the American Museum 

 are teeth of Eocene Primates and Menotyphla : this material 

 was found to be highly fossilized and very friable, and before 

 examining it thoroughly, I decided to complete my collection of 

 tooth sections of recent Primates. A large number of old-world 

 and new-world monkeys have been examined, and some 200 

 sections have been prepared from teeth of practically all the 

 members of the suborder Lemuroidea. 



The results obtained from this microscopical examination 

 disclose certain new featiu^es, which, taken in conjunction with 

 other anatomical characters, should be of value. 



The first striking feature to be recorded is that throughout the 

 whole suborder Lemuroidea a constant feature in the enamel is a 

 regular system of tubes continuovis with the dentinal tubes. 

 Chiromys provides a solitary exception, and thus occupies a 

 position similar to Pliascolonnys amongst the Marsupials. The 

 richness of penetration varies greatly both in the teeth of 

 different families and also in different areas of the enamel of 

 individual teeth *. 



In the Lemuriformes the amount of penetration is usually 

 slight, seldom exceeding the extent shown in PI. II. fig. 2, where 

 the tubes (^) are seen to pass through about half the thickness of 

 the enamel : over the apex of the unworn incisor teeth and in the 

 cusps of the molars the tubes often pass outwards to within a 

 short distance of the free surface, as shown in PI. III. fig, 2. As 

 one passes downwai'ds towards the neck of the tooth and the 

 enamel becomes thinner, the penetration becomes more sparse, 

 most of the dentinal tubes splitting up into a fine bnishwork just 

 beneath the enamel surface. Such tvibes as pass over into the 

 enamel traverse a layer of uncalcified tissue shown in PI. 11. 

 figs. 1 & 2 and designated by the letters %i.l. 



In the Indrisinse the tubular penetration is extremely rich, 

 rivalling the extent found in the Macropodidfe ; for over the 

 apices of the cusps of all the teeth there are tubes in the enamel 

 continuous with almost every dentinal tube, and these pass out- 

 wards through the greater thickness of the enamel. The illus- 

 trations shown in PI. I. figs. 1 & 2 give a cleaier idea of this 

 condition than can be conveyed by a verbal description. 



Towards the necks of the teeth the penetration is still quite 

 rich, but in the sulcuses of the crowns of the molars the pene- 

 tration does not proceed to any great extent. 



In Propiihecus the degree of penetration is markedly less than 

 in the Indrisinse, but in certain areas of the enamel it is a con- 

 spicuous feature (PI. II. fig. 3). 



In the LorisidsB there is a very rich penetration, attaining its 



* For simplicitj' I retain the terms " tube " and "penetration," since they are 

 employed in all- text-books in the description of this condition in the enamel, but I 

 consider the so-called tubes to be fibrils, epiblastic in origin, and though continuous 

 with the dentinal fibrils, they ai'e not a penetration of these structures into the 

 enamel {vide Carter, Phil. Trans. Roy. Soc. ser. B, ccviii. 1917). 



