size, are more divergent, and directed more upwards ; they have
been found of the length of from eight to ten inches, of which the
implanted base measured three-fifths of the entire length of the
tooth, and the crown was one inch and a quarter in breadth ; this is
worn obliquely inwards at its upper enamelled part.
Not a trace of a canine tooth or its alveolus has been observed
in the skull of a mature individual of any existing or extinct species
of Rhinoceros, hut such we must consider the small and simple tooth
(PL 138, fig. 13, c) developed at the fore part of the superior
maxillary bone in the foetal Rhinoceros indiens, two lines in advance
of the alveolus of the first small deciduous molar (p 1) and one
line behind the suture which unites the maxillary with the intermaxillary
bone. The specimen in which I detected this tooth, the
crown of which had pushed through the jaw, but not through the
gum, appeared to be at the full-time, or newly born. The tooth
and its socket must soon disappear, for in the specimen of the
upper jaw of a young Indian Rhinoceros figured by Cuvier in the
‘ Ossemens Fossiles,’ tom. cit. PL v, fig. 3, there is no trace of
the alveolus of the rudimental canine in the tract of bone between
the first deciduous molar and the intermaxillary suture; anterior
to this the intermaxillary bone shows the sockets of the two comparatively
large incisive teeth. This discovery of vestiges of
canines in the genus Rhinoceros shows an additional character,
although a transitory one, linking that genus with the nearly allied
extinct Palæotherium.
The first of the permanent series of seven molar teeth is very
small in both jaws, and is soon shed. The first upper premolar
is notched on the inner side in the one-horned Rhinoceros
(PL 138, fig. 3, p 1) ; the notch sinks deeper and expands
in the African two-horned species ; and in the Sumatran bicorn
Rhinoceros it presents a detached lobe on the inner side : the second
upper premolar is more suddenly enlarged in the one-horned than
in the two-horned Rhinoceros. Before the crowns of these large
and complex premolars and molars begin to be abraded, the
eminences bounding the valleys terminate in sharp enamelled ridges,
the principal extending along the outer border of the grinding
surface, and two others continued from this obliquely backwards
to the inner border, one from the antero-external angle, the other
from near the middle of the outer -wall; the inner terminations of these
two parallel oblique ridges form the summits of the two cones which
constitute the inner half of the crown.(l) Small or secondary ridges project
from the sides of the principal ridges into the intervening valleys,
in extent and number varying according to the species, the most
constant being the one, marked ƒ in fig. 5, from the posterior oblique
ridge. The first effect of mastication is to wear away the enamel from
the summits of the ridges, and to expose a tract of dentine which widens
as attrition proceeds, varying the pattern of the grinding surface as
the valleys are thus progressively obliterated. These changes are
illustrated by the figure of the molar series of the upper jaw of the
Rhinoceros indicus (PI, 138, fig. 3). The chief .valley, marked b in fig. 5,
is expanded and bilobed at its termination, and is deepest at each
terminal division, and at the middle of its course; in the second
true molar (m 2) its entire extent is shown; in the last molar (m 3)
the posterior terminal division is insulated by the wearing away of
the enamel from the shallower part of the valley between the two
divisions : the same insulation has taken place in m 1, and the shallow
entry of the valley is almost worn away; in p 4 it is obliterated,
and the peninsular fold of enamel is converted into an island.
The same change is effected in the short posterior fold c, it deepens
as it penetrates the crown, and in m 4 its beginning has been worn
down to the dentine, and its end converted into an island of enamel.
The same three islands are shown in p 3 and p 2, with the addition
of linear tracts formed by the wearing down of the crown to the
basal ridge at the antero-internal lobe. The grinding surface is
sometimes reduced to a plain tract of dentine before the molar is
shed. There is no posterior fold c in the last molar. (2)
The modifications in the form of the valleys and secondary
(1) See the germ of the upper molar, PI. 138, fig. 8.
(2) These, and similar details in other chapters of this work, may be deemed tediously,
perhaps unnecessarily, minute : they are, however, indispensable to whoever would make successfully
the noble application of anatomy to the restitution of lost species and the past history
of the globe.
Q Q