there, anastomosing, or terminating in the calcigerous or dentinal
cells. (1)
The lateral ramuli are more numerous in the fang than in
the crown; here the finer branches are most abundant at the
peripheral extremities of the tubes, which frequently appear to
end abruptly, as if truncated; sometimes dividing and sub-dividing
quickly , the terminal divisions diverge widely, and appear to end
in the stratum of fine cells which divides the dentine and enamel:
here and there I have seen a tube bending back to form an anastomotic
hoop with an adjoining tube. The peripheral stratum of
minute cells receiving the terminal ramifications of the calcigerous
tubes and forming the boundary between the dentine and enamel,
is the most sensitive part of the dentine: it is not, however, so
distinct a tissue as to merit a special name. (2)
In the bicuspids(3) a larger proportion of the tubes proceeding
from the summit of the pulp-cavity are vertical than in the canines
or incisors, and a still greater proportion in the broad-crowned molars.
(4) The tubes going to the apex of each cusp or tubercle are the
most vertical, and the surrounding tubes begin to incline from
the perpendicular in proportion as they terminate nearer the base
of each cusp: in the interspaces of the cusps, therefore, the tubes
incline towards each other. At the early stage of the calcification
(1) PI. 123, fig. 1, dK These cells, defined in my Report to the British Association in
1838, (vol. v i i , p. 144) as “ calcigerous cells, which form numerous layers generally arranged
parallel with the contour of the cavity of the pulp, and most numerous at the circumference
of the ivory/ are untruly indicated by the exaggerated expression that * the intertubular
substance is cellular’; they would be sought for in vain as cells, in the interspaces
of the tubes. The true dentinal or calcigerous cells include many tubes and intertubular spaces,
and it is much more exact to say that those cells include a tubular structure, than that the
intertubular space is cellular. The unprejudiced microscopical observer will find the tissue
in the intervals of these dentinal tubes, for the most part clear and structureless, as Pur-
kinje and Retzius have rightly described. Dr. Henle has stated that when deprived of the
hardening salts it tears into fibres, whose course is parallel to the tubes: this is not a satisfactory
indication of original structure. Simmering, von Baue des Mensch. Korp. 8vo. 1841
p. 855-856.
(2) M. Duval, who has well described the vital properties of this part of the dentine,
and rightly states it to be the seat of the commencement of caries, has proposed to call it
‘ dictyodonte.’—" Observations Anatomiques sur l’Ivoire,” 8vo. 1839, p. 14.
(3) PI. 122, fig. 4. (4) lb. fig. 6 and J.
of the dentinal pulp, when the cusps are yet distinct from each
other, they constitute so many distinct radiating systems of dentinal
tubes, and the crown of a molar seems to be formed by the
basal confluence of three, four or five simple teeth. At the circumference
of the crown of both premolar and molar teeth, the tubes
incline more and more towards the horizontal direction as they
approach the fangs. In the upper premolars in which the pulp-
cavity divides and is continued in the form of two linear fissures
along the connate fangs,(!) each fissure is the centre of divergence
of radiating tubes, having the same primary and secondary curvatures,
as in the single fang of the incisor and canine. When a
molar is implanted by only two broad and compressed fangs the
pulp-cavity usually divides in each ; and when the last molar is
implanted by an undivided root, the dentinal tubes of that part radiate
also from two distinct pulp-canals. In the base of three-fanged and
four-fanged molars there are as many radiating systems of dentinal
tubes. The terminations of the tubes in the fangs are more frequently
resolved into fine branches than in the crown, and the
communications between these branches and the analogous minute
tubes from the radiated cells of the cement are numerous and plain.
The dentinal cells of the human tooth(2) are sub-circular, about
3^ th of an inch in diameter; they seem most numerous from being
most conspicuous, near the periphery of the dentine, as originally
described by me in the dentine of the Crocodile. (3) They
are best seen in sections of the crown of a permanent tooth
before it has come into place. In a longitudinal section the peripheral
boundary of the cell, or that next the enamel, is most
conspicuous ; it describes a slight curve : the lateral boundaries form
a very open angle: the posterior boundary is formed generally by
the convex curve of the posterior cell which appears slightly to
over-lap the one in front, and in this view of the cells their
transverse diameter exceeds the longitudinal one. In a transverse
section of the dentine the cells’ boundaries are, for the most part
hexagonal, with the angles feebly marked. From the differences
(1) PI. 122, V , V . (2) PI. 123, fig. 1, d>, dK
(3) Report of British Association, 1838, p. 144.