92 A MANUAL OF DENTAL ANATOMY. 



of its walls. Example Lepidosteus,. 

 Labyrinthodon. 



(iii.) Vaso-dentine, dentinal tubes few or 

 absent, but capillary channels with 

 blood circulating through them abun- 

 dant. Example Hake. 



(B.) Dentines developed by calcifications shooting- 

 through the interior of a pulp, not by calcifi- 

 cation of a specialised surface layer of cells, 

 (iv.) Osteo-dentine ; with no true dentinal 

 tubes, but minute tubes analogous to 

 bone canaliculi, and large irregular 

 channels containing pulp-tissue (not 

 blood-vessels only). Example Tooth 

 .of Pike. 



It remains to be added that the same pulp may undergo 

 a change in the manner of its calcification ; that is to say, 

 that after having gone on with surface calcification from 

 an odontoblast layer for a certain length of time, this may 

 give place to a more irregular internal calcification into an 

 osteo-dentine. 



This is especially prone to happen after injury, and is 

 often exemplified upon a large scale in Elephants' tusks ; 

 the pulp of which, normally engaged in calcifying the 

 odontoblast layers into ivory, may after an injury calcify 

 irregularly, and solidify into a coarse osteo-dentine. 



It will then be easy to understand that so-called secon- 

 dary dentine, produced in a pulp which ordinarily forms 

 hard dentine, may partake of the character of vaso- or of 

 osteo-dentine. 



Thus the pulp of a sperm whale's tooth becomes oblite- 

 rated by a development of secondary dentine, which some- 

 times forms irregular masses loose in the pulp chamber, and 

 sometimes is adherent to and continuous with the dentine 



