1906.] 



TEETH OP 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 Thylacimis (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-fig. 13. 



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

 halfway through the enamel. 



Text-fiff. 14. 



Das^jtrMS.— Longitudinal section of dentine and enamel. 



tha,n 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 traced by careful illumination right in to the 

 Piioc. ZooL. See— 1906, YoL. I. No. IV. 4 



