I have not observed this transition. If it really so happens,
then the cavities of the cells so completely disappear, as to leave
no trace of the cartilage-corpuscles. From the observations
of Retzius it might be supposed that some of the cells retained their
cavity and even were converted into radiated cells, since Retzius
observed true bone corpuscles in the dentine. If, then, the superficial
layer of the pulp, consisting of cylindrical cells, is converted
by ossification into the dentine, then the subjacent layer of the pulp’s
parenchyme, consisting of round cells, must first be converted into
cylinders, the vessels of this layer become obliterated, and this layer
then become ossified, &c.
“ What then are the dentinal tubes? Retzius compares them
with the calcigerous tubes that radiate from the bone-corpuscles, and
I was at first of the same opinion, and accordingly I regarded them
as prolongations of the cells, the bodies of which lay in the pulp. If
the pulp be drawn out of the pulp- cavity of a hog s tooth and the
margin of the pulp be examined, it is seen that each of the superficial
cylindrical cells is prolonged, opposite the dentine, into a short fine
fibre and that these fibres correspond in diameter with the dentinal
tubes projecting from the surface of the pulp. I once believed that
they projected into the dentinal tubes, and that the intertubular tissue
was merely the intercellular substance between these elongations
of the cells. But I have given up these ideas since I observed nothing
of the kind in human teeth, and since this explanation brings with it
a difficulty in regard to the teeth of the pike. In these teeth, according
to Retzius, there is a direct transition from dentine to bone.
If one of the large teeth of the lower jaw be sawed off, the earth
dissolved by muriatic acid, and fine longitudinal sections removed,
the dentine is seen to form a hollow cone which is filled by bone.
The dentine is transparent and consists of fibres which proceed from
the point to the base of the cone. The bone is traversed by canals,
which resemble the medullary canals of ordinary bone, except in
being less regular. The dentinal tubes are connected with these
medullary canals of the proper osseous substance, and it is plain
that the tubes are continued funnel-wise from the medullary canals.
The canals ramify in the dentine and as they proceed transversely
across the thickness of the tooth-cone, so they decussate the dentinal
fibres. Accordingly here the dentinal tubes correspond with the
medullary canals of bone not with the calcigerous tubes which radiate
from the bone-corpuscles.
“ A more certain knowledge of the whole structural relations of
dentine seems to be only possible when its development is studied in
very differently constructed teeth.”(1)
The main facts, then, which may be considered as established by
the researches of Purkinje and Schwann, relative to the formation of
dentine and the changes which the dentinal pulp undergoes during
that process are the following : the proper tissue of the pulp consists
of minute nucleated cells, with capillary vessels and nerves, invested
by a dense structureless membrane (2) which disappears during
the formation of the dentine. The superficial pulp-cells assume
an elongated form; they correspond in diameter and
direction with the tubes of the contiguous cap of dentine. These or
similar cells are observed, in a state of transition into dentine, in the
interspace between the pulp and the previously formed cap of dentine
; they adhere to the latter when it is displaced from the pulp.
(1) Schwann, loc. cit. p. 128.
(2) The capsule of the entire dental matrix will be understood to be quite a distinct part
from the * preformative membrane | of the pulp.