1906.] 



TEETH OF CREODONTS. 



49 



it is difficult to see the outline of the enamel prisms, which, 

 however, where traceable pursue a nearly straight course. 



When, however, we come to the enamel of Thylacmus (text- 

 fig. 13), we find that the tubes thin out and are lost before they 

 reach the exterior of the enamel, even where this is thickest, 

 though sections may be found in which they penetrate further 



Text-fi^. 13. 



Thylacinus. — Longitudinal section of dentine and enamel. The tubes reach 

 halfway through the enamel. 



Text-fi^. 14. 



Dasyiinis. — Longitudinal section of dentine and enamel. 



than in that figured. And where there is a tolerably abundant 

 passage of tubes, the so-called granular layer, which marks the 

 exterior of Placental dentines {cf. text-fig. 15, p. 50), is absent or 

 but little conspicuous. Outside the region of the tubes the enamel 

 prisms are fairly distinct and are seen to be straight ; the straight 

 prisms may also be ti-aced by careful illumination right in to the 

 Pkoc. Zool. Soc— 1906, Vol. T. No. IV. 4 



