48 



MR. C. S. TOMES ON THE 



[Jan. 16, 



The enamel is most lichly tubular in the Diprotodont gi'oup ; 

 though it must not be thought that the tubes are sparse in the 

 Polyprotodonts. In a large nvTmber of instances there is a slight 

 dilatation at the point of junction of the dentinal tube with the 

 enamel tube, a sort of clumsy joint in fact (text-fig. 12) ; but this 

 is not an invariable character, the tube sometimes passing on with 

 no mark at the point of junction. "Where, however, the enamel 

 thins out towards the neck of the tooth, the tvibes in it, whether 

 it be that of a Diprotodont or a Polyprotodont, become few or none, 

 so that it is necessary to be careful not to select the enamel to 

 be examined from this situation. 



As illustrations of typical marsupial enamels I have selected that 

 of Hypsiprymnus (text-fig. 12), of Thylminus (text-fig. 13, \^. 49), 

 and of Dasyurus (text-fig. 14, p. 49) ; those interested in the subject 



Text-fig. 12. 



All the figures, tliougli drawn from actual slides, are semi-diagrammatic. 



ITi/psiprymnus. — Longitudinal section of dentine (D) and enamel (E). The tuhes in 

 the enamel reach its outer surface, or nearly reach it. Slight dilatations mark 

 the passage from the dentine to the enamel. 



will find figures from other genera in the paper of my father's 

 already referred to. "With regard to these and the other figui-es 

 illustrating this paper, I may say that for the sake of clearness 

 they are semi-diagrammatic. Though all have been drawn from 

 actual sections, fewer tubes have been drawn than actually exist in 

 a given ai-ea, and all indications of structure, other than those 

 with which we are immediately concei-ned, have been left out. 



In the Diprotodont Hypsiprymnus (text-fig. 1 2) the enamel tubes 

 are seen in their greatest development. Starting, usuall}^ with a 

 dilatation at that point, from the dentinal tubes they traverse 

 the entire thickness of the enamel, turning a little to one side as 

 they approach its periphery, and some of them branching ofi" 

 almost at right angles. It must, however, be rinderstood that 

 had the section been taken from the thin enamel near the neck 

 of the tooth, fewer tubes, and finally no tubes at all, would have 

 been seen. Where the tubes are very abundant, as in this case. 



