470 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. 



structure of the dentine. The interglolndar substance is in the first 

 place a structure tolerably widely distributed. Ozermak has described 

 under this name those parts of the dentine which, when thin sections 

 are dried in air, appear beset with irregular spaces and cavities. The 

 walls of these spaces, especially if they form a deep notch, often pro- 

 ject in the form of spheroidal masses or dentinal globules. Indica- 

 tions of a spherical form which sometimes occur in the compact 

 dentine are explicable on the supposition that the interglobular spaces 

 have been obliterated by calcification of their soft contents, the 

 contours of their original walls being to some extent retained. The 

 contents of the interglobular spaces consist of a soft mass. In the 

 young fresh teeth of the calf, rounded and stellate cells may frequently 

 be seen in the larger interglobular spaces, with processes which extend 

 into the dentinal canals opening into them. At a later period the cells 

 atrophy, or their protoplasm becomes converted into a substance 

 analogous to the dentinal cartilage. In immediate proximity to the 

 cement, a layer of very small, closely compressed interglobular spaces 

 is very constantly present, forming the granular layer of Tomes. The 

 interglobular spaces, with their soft contents, are therefore only the 

 result of a somewhat irregular process of dentinification, and are 

 analogous to the small irregular medullary cavities found in the interior 

 of compact bone. 



In the dentine of many animals, especially of Fishes, of some Ro- 

 dents, in the central portion of the tusks of the Elephant, the molar 

 teeth of the Iguanodon and others, vascular canals exist analogous 

 to the Haversian canals of bone, constituting the vaso-dentine of Owen. 

 In Man this form of dentine is only met with as a consequence of the 

 secondary ossification of the pulp. In many Fishes (Kolliker, 45) 

 the bones of the skeleton consist in great part of true dentine ; whilst 

 conversely we find in the dentine of the teeth, especially in pathological 

 conditions, masses with bone lacunae, termed Odontomes by Virchow, and 

 Osteo-odontomes by Hohl, which occur in the dentine near the cement, 

 or in ossifications of the pulp, and form the osteo-dentine of Owen. 



Transitional forms, between vaso-dentine, osteo-dentine, and ordinary 

 dentine, are frequently met with in Fishes, as, for instance, in the Pike. 

 In the Cetacea, Dugong, and Physeter, again, the peripheric layer of the 

 dentine, which contains a large number of small interglobular spaces 

 and true bone corpuscles, passes without interruption into the invest- 

 ing cement, so that it is impossible to draw here any definite line 

 between osseous substance and dentine. 



Schreger (7) first recognised a system of concentric lines running 



