diate or inter-tubular tissue ; this he describes as homogeneous and
without structure, and as entering into the composition of the dentine
in a greater proportion than the tubes themselves.
The more extensive, varied and minute observations of Professor
Retzius led to the discovery of the cells of the intertubular
tissue, of the ramuli sent off from the main calcigerous tubes
into that tissue, and of the anastomoses of the ramuli with each other,
with the intertubular cells, and with the cells at the periphery of
the dentine. According to the researches of Dr. Schwann the
animal basis of the intertubular tissue possesses a fibrous structure.
Besides the primary and secondary branches of the calcigerous
tubes Retzius first clearly^described their curvatures and undulations,
which may he defined as follows : as a general rule the dentinal
tubes are directed, as affirmed by Leeuwenhoek and Purkinje, from the
inner to the outer surface of the tooth, and vertically to those surfaces
; hut in their course the tubes describe two, three, or more
curvatures, appreciable by a low magnifying power: these I have
termed the ‘ primary curvatures.’(1) With a higher power, the tubes
are seen to he bent throughout the whole of their flexuous course into
minute and equal oblique undulations or gyrations, two hundred of
which were counted by Retzius un one tenth part of an inch’s length
of a human calcigerous tube ; these I have termed the ‘ secondary
curvatures’ or gyrations.(2) Both the primary and secondary curvatures
of one tube are usually parallel with those of the contiguous
calcigerous tubes, and from the radiated course of these tubes they
occasion the appearance of lines running parallel with the external
(1) Trans. Brit. Assoc, vol. vii, p. 148. See Plates 24, fig. 1; 64 a , fig. 2 ; 74, fig. 1; 94.
(2) Ibid, p. 141. See Plates 16, fig. 3 ; 24, fig. 2 ; 64 a , fig. 3*
contour of the tooth ; for, when the surface of a longitudinal section
of a tooth is viewed with the naked eye, the light is differently reflected
from the different parts of the oblique secondary curves of the
tube on which it falls; but the curves being parallel to each other and
to the superficial contour of the section, they appear like the cut
edges of a series of parallel and super-imposed lamellae. In many
teeth, moreover, and especially in the tusks of the elephant, the secondary
branches of the dentinal tubes dilate into intertubular cells
along lines, which in like manner are parallel to the coronal contour
of the tooth; hence another cause of the appearance of concentric
lamellae and of the actual decomposition of such teeth into super-imposed
lamelliform cones.
Such appearances and modes of decomposition are peculiar to
the dense or unvascular dentine; but are by no means common to
that modification of the tissue. They are never witnessed in any of
the varieties of vascular dentine. (1) The prolongation or persistence
of cylindrical canals of the pulp-cavity in the dentinal tissue, which
is the essential character of vascular dentine, manifests itself under a
variety of forms. In mammals and reptiles these canals, which I have
termed ‘medullary’(2) from their close analogy with the so called canals
of hone, are straight and more or less parallel with each other | they
bifurcate, though rarely • and when they anastomose, as in the megatherium,
it is by a loop at, or near, the periphery of the vascular dentine.
In the teeth of fishes, in which the distinction between the dentinal
. (1) This substance was first characterised as a component of tooth, ' distinct from ivory,
enamel, cement, and true bone, and as easily recognisable,* in my paper communicated to thé
British Association, in 1838; loc. cit. p. 137.
(2) Ibid.
b