DESCRIPTION OF THE PLATES.
PLATE L
Diagrams of the development of the dental
tissues. Fig. 1.—Dentine : a, end of a
linear series of primary dentinal cells ;
a', nucleus ; b, division of the nucleus ;
c, c, subdivision and elongation of the nucleolar
matter, establishing secondary cells;
d, elongated nuclei of secondary cells
uniting end to end to form the areæ of
the dentinal tubes ; e, e, calcified cap of
dentine formed by intus-susception of the
clear hardening salts into the walls and
cavities of the cells, and intercellular
blastema, e• ; and by their partial exclusion
from the moniliform nucleolar
tracts, ƒ g, union of two peripheral
nucleolar or secondary cells with one
nearer the centre of the pulp. Fig. 2.
—Inner surface of a portion of the calcified
dentinal pulp, forming the cap
of dentine, which has been displaced :
a, intervals and walls of primary dentinal
cells (‘ aréoles’ of the French Academicians)
; b, indication of walls of secondary
cells forming the parietes of dentinal
tubes ; c, nucleolar matter which establishes
the areæ of the dentinal tubes,
(' granulations des aréoles signalée, par M.
H. Owen,’ of the French Academicians).
For clearer demonstration, the number
of tubes in the areæ of the cell is made
less than in nature. Fig. 3.—Thin calcified
portion «, resting on b, uncalcified
portion of the pulp ; magnified on half
the scale of the preceding scheme. Fig. 4.
—Enamel: h, primary cells suspended
in fluid blastema g ; i, the same angularly
aggregated to form the actinenchymatous
tissue; j , the same, becoming cylindrical
by either elongation or terminal confluence,
k, the nucleus disappearing; l, the modified
prismatic cells, in which the clear
hardening salts are impacted, forming the
spiculse and fibres of enamel; magnified
on the same scale as figs. 1 & 2. Fig. 5.
—^Cement: m, primary cells; p, their
granular nucleus; n, more minutely
granular blastema; n', the same, impregnated
with the ossific sa lts; o, the
primary cell enlarged and receiving the
hardening sa lts; p ', the nucleus altered,
apparently by pressure of the surrounding
salts, and sending out prolongations
or rays; magnified on the same
scale as fig. 4.
PLATE II.
Magnified view of the vascular plexus of
the outer layer of the dental capsule
of the incisor of a Calf (Bos Taurus).
♦The same, nat. size. The centre circle
shows the divided vessels that penetrate
the dentinal pulp. At two parts, a a,
were groups of minute capillaries, in which
the blood appeared to be stagnated, and
the vessels in progress of obliteration :
the cells of the capsule had begun to be
calcified at both these parts, and a thin
layer of cement to be formed.