cavity was divided at its upper part into two conical prolongations, one
for each of the principal lobes of the crown. A few vascular canals
were continued from the apex of each cone into the two sub-divisions
or plates of each lobe.
The dentinal tubes which radiate from the pulp-cavity and its
prolongations, are as remarkable as those of the tusk for their minuteness
and closeness of arrangement; but, in the tooth examined, they
presented at only a few points secondary undulations approaching
in extent to those which characterise the tubes of ivory. A few
tubes from the end of the vascular canal in the centre of the cone
of dentine go straight to the summit of that cone; the rest diverge
from the vascular canals and apex of the pulp-cavity to the sides
of the cone of dentine, with one general primary curve, whose
convexity is turned towards the centre and summit of the cone, the
terminations of the tubes being slightly bent in the opposite direction
: in the roots the dentinal tubes pass, as usual, almost transversely.
The places where the tubuli exhibited the strong secondary
undulations were along a contour line at the middle of the dentine.
At their commencement the tubuli are straight, they then fall into
slight waves, and after forming three or four stronger ones at the
middle of their course, again resume the more feeble and irregular
undulations : their close arrangement renders it difficult to distinguish
bifurcation from decussation; yet in some parts I had clear
evidence of division of the main tubes, which left little doubt that
the usual dichotomy prevailed, to produce the same dense arrangement
of tubuli at the broad peripheral as at the narrower central
part from which the tubes diverge.
The number of minute lateral branches is extreme; especially
in the peripheral third part of the tube. Those from near the usually
bifurcated terminations of the tubes are lost in the stratum of minute
opake cellules near the outer surface of the dentine. Many of the
terminal bifurcations of the tubuli here bend back, and form loops
by anastomosing with adjoining branches.
The fibres of the enamel present a minutely jagged, or cre-
nate outline, but are not crossed, by transverse lines. Their
diameter is ggth of an inch: they are much less wavy than in the
human teeth. The enamel fibres cross the plane of the layer
on a less transverse direction than that of the ends of the tubes
of the dentine directed towards the enamel: the outer surface to
which the cement is attached, shows more pits and irregularities
than that attached to the dentine.
A well-defined layer of cement covers the bottom of the crown
at the interspaces of the two fangs, and extends over these to their
extremity. The sub-circular or full-elliptic radiated cells are closely
arranged, with their long axes parallel with the surface of the
cement; numerous minute cemental tubuli run parallel to that surface,
and communicate with the radiated tubes of the cells and
with the terminal ramifications of the dentinal tubuli. The larger
vascular canals are present only in the thicker deposit of cement
at the bottom of the interspaces of the coronal plates.
Dr. Falconer having kindly permitted me to take a longitudinal
section from a rare specimen of the first upper molar of the Elephas
planifrons, one of the extinct species whose remains he has discovered
in the Himalayan tertiary beds, I am able to give the following
comparison of the microscopic structure of this tooth, and that of
the nearly allied existing Indian Elephant.
The dentinal tubuli are as minute and as closely aggregated ; they
have the same general direction and primary curve ; in parts of the
dentine, as at the summits of the conical sections of the lamellar
divisions of the crown, their secondary undulations are as minute
and irregular; but the number of the strong undulations along the
contour lines at the middle of the dentinal cone is greater. The
strongest contour lines are accompanied by the strong undulations,
but there are many other lines which appear to be formed by a
slight opacity of the basal substance as in the Rhinoceros.
The stratum of opake cellules near the peripheral ends of the
tubes is thicker ; the terminal bifurcations and occasional anastomotic
loops are the same as in the Indian Elephant. The enamel is thicker,
and the component fibres are more flexuous in the El. planifrons,
but in their size and other characters they agree with those of the
recent species. The cells of the cement which covers the crown and