466 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. 



Fishes, as, for example, in the Pike, a common arrangement is the 

 combination of a central mass of vascular dentine (vaso- dentine, 

 Owen), with a thin cap of ordinary dentine, which in the most 

 external layers is homogeneous, and very hard (vitro -dentine, Owen, 

 84). Compare fig. 99. 



DENTINE (Substantia Eburnea, Ebur). Dentine forms a 

 yellowish- white, highly elastic, but friable mass, presenting a 

 finely fibrous, peculiarly lustrous fracture, and is one of the 

 hardest constituents of the animal body. Its chief components 

 are a very firm matrix, analogous to compact bony tissue, and 

 extremely fine, frequently branched fibres the dentinal fibres 

 of Tomes (40) and Kolliker (58), which occupy fine canals, the 

 dentinal canals traversing the matrix. The dentinal fibres are 

 enormously elongated processes of the the so-called dentinal cells, 

 or cells of the dentinal pulp (odontoblasts). Dentine conse- 

 quently corresponds to bone, with this difference, that instead of 

 cells it contains the long processes of cells in its calcified matrix. 

 In regard to the other characters of the matrix, it presents a 

 similar uniformity of appearance, and a similar chemical com- 

 position, to that of compact bone. After treatment with acids 

 (especially with dilute hydrochloric acid) a material, dentinal 

 cartilage, is obtained which is precisely similar to ossein, except 

 that it is of somewhat firmer consistence. 



The dentinal fibres constitute the soft parts of dentine. They 

 do not lie in direct contact with the hard matrix, but are 

 invested by sheaths, the dentinal sheaths of E. Neumann (48), 

 which are intimately connected with the matrix. After the 

 fibres have been removed by maceration, or by incineration of 

 the tooth, the dentinal sheaths remain, and even after destruc- 

 tion of the matrix by boiling in strong muriatic acid or in 

 caustic alkalies, they constitute the only perfectly indestructible 

 residue of the tooth. They form the white finely fibrous felt 

 which still remains after treatment with the above-mentioned 

 reagents. The dentinal sheaths, it is highly probable, belong 

 to the category of elastic limiting layers which not unfrequently 

 form around the cavities of the connective tissues. E. Neumann 

 considers them to be calcified (see also p. 125). 



The dentinal matrix, then, is traversed by a number of fine 



