In the cells of the dentinal pulp the nucleus fills the parent
cell with a progeny of nucleoli before the work of calcification
begins: in the enamel-pulp the nucleus of the cell disappears, like
the cytoblast of the embryo plant in the formation of most vegetable
tissues: in the cells of the capsule, the nucleus neither perishes nor
propagates, but retains its individuality, and gives origin to the
most characteristic feature of the cement, viz : the radiated cell.
The primordial material of each constituent of the tooth-matrix
is derived from the blood, and special arrangements of the bloodvessels
pre-exist to the development and growth of the constituent
substances. A pencil of capillaries is directed to a particular spot
in the primitive dentiparous groove, and terminates there by a looped
net-work, from which spot a group of nucleated cells begins to
arise in the form of a papilla. The cells of the papilla are, however,
colourless, and the plexus of capillaries is confined to its base.
In the Mammalia (embryo Calf of three inches in length) membranous
septa are formed, into which the vessels extend, which cross
the groove and inclose the papilla in a follicle. From the free
margin, of this follicle the processes are developed, which indicate
the configuration of the future crown of the tooth, and, in the
molars of the calf, subsequently develope the re-entering folds on
which the complex structure of the crown of the molar tooth
depends.
The primary dentinal papilla and its capsule rapidly increase
by successive additions of nucleated cells, apparently derived from
material supplied by the capillary plexus at the base ; the capillaries
now begin to penetrate the substance of the pulp itself, where they
present a sub-parallel or slightly diverging penicillate arrangement,
but preserve their looped and reticulate termination near the apex
of the pulp. Fine branches of nerves accompany the capillaries
and terminate also in loops.
The primary cells of the papilliform pulp, the “ grana aequalia
globosa” of Purkinje, are described by him as pre-existing to the
appearance of vessels and nerves in the pulp ; they are undoubtedly
unaccompanied by the blood-vessels at their first aggregation to
form the papilla; but they bear the same relation to the capillary
net-work at the base of the papilla, which the subsequently formed
cells do to the capillaries that extend into the substance of the
papilla or pulp, when it is more developed. The primary cells
and the capillary vessels and nerves are imbedded in, and supported
by a homogeneous, minutely sub-granular, mucilaginous
substance, the ‘ blastema.’ The cells (PI. 1, fig. I , a) which are
smallest at the base of the pulp, and have large, simple, subgranular
nuclei (ib. a'), soon fall into linear series directed towards the periphery
of the pulp: where the cells are in close proximity with that
periphery, they become more closely aggregated, increase in size,
and present the following changes in their interior. A pellucid
point appears in the centre of the nucleus which increases in size
and becomes more opake around that central point, rendering the
compressorium requisite for its demonstration. A division of the
nucleus in the course of its long axis is next observed (ib. b). In
the larger and more elongated cells, still nearer the periphery of the
pulp, a subdivision of the nuclei has taken place, and the subdivisions
become elongated with their long axes vertical or nearly so to the
plane of the pulp, and to the field of calcification (ib. c). The
subdivided and elongated nuclei become attached by their extremities
to the corresponding nuclei of the cells in advance ; and the
attached extremities become confluent (ib. d). Whilst these changes
d 2