DEVELOPMENT OF VASCULAR DENTINE. 
39 
of the teeth, I find (in the case of Sargus, the only one which I have been able to 
procure fresh, or preserved from the first in chromic acid) that the exserted and 
implanted portions of the teeth are alike developed from the same dentinal pulp (see 
k in fig. 23), and, what is somewhat remarkable, I cannot detect any difference in 
structure between that upper portion of pulp which is engaged in forming hard dentine, 
and that lower portion which is building up vaso-dentine, save only that this latter 
part is more richly vascular. Why the pulp should at a particular point cease to 
form “ hard ” dentine, I cannot see ; possibly had I been successful in making an 
injection, which I attempted, but failed in effecting, the distribution of the vessels 
might have explained it. 
In the implanted portion, near to the point where the change takes place (see figs. 
19 and 20), the pulp is furnished . with odontoblasts, and the dentine formed is the 
vaso-dentine with a few true dentinal tubes, the large channels being the spaces left 
for and occupied by capillaries. Lower down no dentinal tubes occur, and the 
dentine presents the appearance represented in fig. 2 1 , whilst in a fully completed tooth 
we find near to the end of the root the shell of vaso-dentine ( d ' in fig. 1 8) becoming 
thinner and thinner, whilst instead of its surrounding a central pulp chamber, this 
latter is blocked up by a coarsely reticulated calcified tissue (see also base of the left hand 
tooth in fig. 23). It is hard to say where the tooth ends, for the vaso-dentine thins 
out to nothing, and the coarse bone of the axial portion merges into that which 
surrounds and underlies the tooth, and serves to secure it by anchylosis to the walls of 
its socket (c in fig. 23 .and 19). In the development of these teeth we have therefore 
a single dentinal pulp which at its apical part forms true or hard dentine ; at a certain 
point it changes somewhat abruptly, and forms vaso-dentine, and then by more insen- 
sible gradations its axial parts, and finally its whole base, change their manner of calci- 
fication, and become converted into an osteo-dentine which blends insensibly with that 
coarse bone which is being formed outside the limits of the tooth pulp. No other tooth 
with the development of which I am acquainted shows with the same clearness as the 
tooth of Sargus, the relation of these several tissues to one another and to bone. 
It appears to me exceedingly undesirable to multiply names, so in the place of doing 
so, I would suggest merely rendering more precise and more limited the meaning 
attached to the terms Vaso-dentine, Osteo-dentine, and Plici-dentine, to the latter 
of which, however, a more extended application than it has hitherto had must be given. 
To summarise the result of the foregoing observations, we should distinguish four 
varieties of dentine, to be thus described : — 
I. Hard unvascular Dentine ; a tissue wholly developed from the odontoblast 
layer of the dentinal pulp, and permeated by a system of dentinal tubes radiating from 
a central pulp chamber. Example ; Human Tooth. This passes through gradational 
forms, such as that met with in the Serrasalmo (fig. 11*) and the Flounder (fig. 10*), 
into typical 
II. Vaso-dentine • a tissue without true dentinal tubes, although it is wholly 
