their perennial growth by constantly reproducing the matter to replace
the abraded extremities. The direction of the abraded surfaces is
in part provided for by the partial disposition of the enamel: in the
upper median incisor this is laid upon the fore and outer part of
the tooth: in the lateral incisor there is a narrow strip of enamel
along the convex side of the tooth. The enamel is soon entirely
worn away from the crowns of the lower incisors ; but it is persistent
in the canines, where it extends to the end of the implanted
base; in the upper canine being laid upon the posterior and outer,
and not on the fore part, whilst its position is reversed upon the
inferior canine. The grooves and ridges upon the enamel of this
tusk are strongly developed : most of them are longitudinal, but the
prominent anterior part of the outer surface is traversed by a series
of oblique ridges; and strongly marked transverse grooves and
ridges cross the tusk at irregular distances, apparently indicating
epochs of the eruption of the tusk.
The molar series consists of p. Q , m. §E|, = 28.(1) The first
premolar has a simple subcompressed conical crown and a single
root: it rises early, and at some distance in advance of the second
premolar, and is soon shed, the other premolars form a continuous
series with the true molars in the existing species ; but in the extinct
Hippopotamus "major, whose remains are found in the superficial
deposits of this island and on the continent, the second premolar is
in advance of the third by an interval equal to its own breadth. This
and the fourth premolar retain the simple conical form but with
increased size, and are impressed by one or two longitudinal grooves
on the outer surface, which when the crown is much worn give a
lobate character to the grinding surface : there is a strong tuberculate
ridge on the inner and hinder part of the base of the crown, and in
the anterior premolars the ridge on the fore and back part of the
cone, extending to the summit of the crown is notched or
tuberculate near its base. In the premolars of apparently the
Hippopotamus minor figured in the work of Scilla ‘De Corporibus 1
(1) M. Fr. Cuvier assigns | fausses molaires I-, molaires t, to the genus Hippopotamus
in the | Dents des Mammifères’ p. 206; but the first molar was shed and the last deciduous
molar was not shed in the lower jaw of the specimen which he figures and describes, whence
the mistake.
marinis,’ tab. xii, fig. 1, (1747) the notches extend to the summits of
these ridges. I have given an original figure (Pl. 142, fig. 3) of one
of these problematical teeth, from the specimen which now forms
part of the Woodwardian Collection at Cambridge, by the kind
permission of the eloquent Professor of Geology in that University;
the anterior border is not so regularly notched as in Scilla’s figure;
and the two fangs shew the moderate proportions of those of the
premolars of the Hippopotamus, and by no means the ventricose
character of the roots of the teeth of a seal, to which family of
Carnivora this ancient fossil has been referred (2).
The true molars are primarily divided into two lobes or cones
by a wide transverse valley, and each lobe is subdivided by a narrow
antero-posterior cleft into two half cones, with their flat sides next
each other; the convex side of each half cone is indented by two
angular vertical notches, bounding a strong intermediate prominence,
the analogue of that which rises out of the outer depression of the
Ruminant’s molar (PI. 134, fig. 3, o o) : a strong ridge bounds the
fore and the back part of the base of the crown and extends
completely round the last upper molar. A view of the unworn
summits of the crown of a true molar of the Hippopotamus is given
in Pl. 143, fig. 3. When these summits begin to be abraded each
lobe or pair of demi-cones presents a double trefoil of enamel on the
grinding surface: when attrition has proceeded to the base of the
half cones, then the grinding surface of each lobe presents a
quadrilobate figure, as shown in Pl. 143, fig. 4. The crown of the
last molar tooth of the lower jaw is lengthened out by a fifth cone,
developed behind the two normal pairs of half cones, and smaller
in all its dimensions. The enamel on all the molars of the
Hippopotamus is thick and has a wrinkled and punctate exterior.
The three last persistent premolars have each two fangs in both jaws.
The true molars have four fangs, except the last below, which has five.
Extinct Hippopotamidec.—The fossil Hippopotamus major adheres
closely to the type of the dentition of the existing species, the most
marked distinction being the diastema between the second (first per-
(2) It is the Phoca dubia melitensis of M. de Blainville, ‘ Osteographie de Phoca, 4to. p. 46 ;
apparently on the authority of M. Agassiz, p. 44.