DEVELOPMENT OF VASCULAR DENTINE. 
27 
the third in which the dentine is permeated by a network of medullary canals, of 
which the interspaces are occupied by the calcigerous tubes and cells. The canals 
ramify and anastomose abundantly, as in Lamna, and in the Percoid, Lucioid, and 
Gadoid families. 
In his ‘Anatomy of Vertebrates'' (vol. i. p. 361), he says: “The simplest 
modification of dentine is that in which capillary tracts of the primitive vascular pulp 
remain uncalcified, and permanently carry red blood into the substance of the tissue. 
“ These so-called ‘ medullary ’ or ‘ vascular * canals present various dispositions 
in the dentine which they modify, and which is called ‘ vaso-dentine.’ 
“ A third kind of dentine is where the cellular basis is arranged in concentric 
layers around the vascular canals, and contains ‘ radiated cells/ like those of 
osseous tissue ; it is called ‘ osteo-dentine.’ The transition from dentine to vaso- 
dentine, and from this to osteo-dentine, is gradual, and the resemblance of osteo- 
dentine to true bone is very close.” 
Hertwig (Ueber Bau und Entwickelung der Placoidschuppen und der Zahne der 
Selachia. Jenaische Zeitschrift, 1874), in describing the dentine of Shark’s teeth 
speaks of the frequent absence of a definite pulp-cavity, its place being taken by a 
canal system containing cells and blood-vessels. He notes the absence of a definite 
odontoblast layer upon the formative pulps of either teeth or scales (which are 
practically speaking the same in these respects), but says that the cells which do 
lie upon the surface, though not forming a very sharply defined layer, play the part 
of odontoblasts. He also compares their method of calcification to that of osteoblasts, 
and notes the occurrence of similar cells in the larger canals far within the 
formed dentine. 
His description of the dentine met with in these scales and teeth, as well as of 
their development, would bring the tissue so formed within the restricted meaning 
which I have proposed in the following pages for the term osteo-dentine, a result 
at which I had myself arrived. 
The foregoing extracts, few though they are, embody most of the facts of 
importance which I can find upon record ; and what little mention is there made of 
the relation of vascular dentine to the formative pulp and of the contents of its larger 
tubes, appears not to have been grounded upon observation so much as upon d 
priori deductions. 
As I shall endeavour to show, the study of their development must lead to the 
discrimination of at least three varieties of vascular dentine, but since the terms 
vaso-dentine and osteo-dentine are in common use, it will be far more convenient 
to retain them instead of introducing new terms, merely limiting and rendering exact 
their application, which is at present as vague as it well can be. For the third 
variety also a name already in use may be found which will describe its nature with 
sufficient accuracy. 
