DENTINE 257 



scattered vascular tubes appear, and in the lower portion 

 of the tooth there are no dentinal tubes, but a typical vaso- 

 dentine has taken their place. From this, as Tomes says, 1 

 ' it may be learnt that hard dentine and vasodentine are 

 not fundamentally dissimilar, and that they may pass into 

 one another by imperceptible gradations, so that it cannot 

 be said exactly at what point the name of vasodentine is to 

 be given to it '. The teeth of the extinct Megatherium show 

 a regular system of vascular canals on the inner portion of 





FIG. 159. Vasodentine of Hake (Gadus Merluccius) showing thorn-like 

 projections and longitudinal striation of the matrix. ( X 150.) 



the dentine terminating at a definite line, the rest of the 

 tissue being made up of tubular or ortho- dentine. The 

 outer part of the dentine of the Manatee shows forms which 

 have the general appearance of vascular loops, but con- 

 siderably modified by the encroachment of calcification 

 upon them, the rounded contours of the margins suggesting 

 a resemblance to elongated interglobular spaces (Tomes). 



From the evolutionary standpoint the above observations 



are of considerable interest ; it is an undecided question 



whether the ancestral form of dentine was of the tubular 



or vasodentine variety. They seem to exist side by side 



1 C. S. Tomes, Dental Anatomy, 7th ed. ; p. 94. 



MUMMERY g 



