subcubical, and the grinding surface, when moderately worn, subquadrate,
and penetrated by two folds or valleys of enamel: the
principal valley (Pl. 138, tig. 5, b) commences at the middle of the
inner side, and extends obliquely outwards and forwards towards
the antero-external angle of the crown about two-thirds across,
where it terminates, according to the species, in a more or
less expanded, sometimes bilobed, cul de sac, (e); the second
and shorter valley (ib. c) is usually of a triangular form, and
indents more or less deeply the posterior border of the crown :
in most Rhinoceroses this is wanting in the last molar, which has
a trihedral conical crown: both valleys are usually deepest at their
blind terminations: the outer surface of the crown is gently undulated
by one of the convexities (ib. o') being sometimes produced
into a longitudinal ridge. In the lower jaw the molars (ib. fig. 9)
have an oblong, laterally-compressed crown, divided into two crescentic
lobes, placed obliquely, with their convexities (o o) outwards
and a little backwards; the anterior horn of the hinder crescent,
before it is worn down, abuts against the middle of the convexity
and below the upper margin of the crescent in front.
The normal formula of the molar series is :—p. jzf, m. jjEf: — 28.
There are no canines. As to the incisors, the species vary not only
in regard to their form and proportions but also their existence -T and
in the varieties of these teeth we may discern the same inverse
relation to the development of the horns which is manifested by the
canines of the Ruminants. Thus, the two-horned Rhinoceroses of
Africa, which are remarkable for the great length of one(l) or both(2)
of the nasal weapons, have no incisors in their adult dentition (PI. 138,
fig. 2); neither had thatgreat extinct two-horned species (Rh. tichorhinus),
the prodigious development of whose horns is indicated by the singular
modifications of the vomerine, nasal, and intermaxillary bones
in relation to the firm support of those weapons.(3)
The Sumatran bicorn Rhinoceros, combines with comparatively
(1) Rhinoceros hicomis, Rh. simus.
(2) Rh. Keitloa, Smith.
(3) These hones in the fossil skull of the species cited are confluent with each other,
forming a solid obtuse termination to the upper jaw, and are anchylosed to a strong bony
partition wall extending from the vomer to the anterior outlet of the nasal passages, and thus
small horns, moderately developed incisors in both jaws ; and the
same teeth are present in the nearly allied extinct two-horned Rhinoceros
called after its discoverer Schleiermacher. The incisors are
well developed in both the existing unicorn Rhinoceroses, Rh. indiens
and Rh. sondaicus ; but they attain their largest dimensions in the
singular extinct hornless species, the Rhinoceros incisivus of Cuvier,
which makes the transition to the extinct genus Paloeotherium, and
forms the type of the aberrant subgenus Acerotherium of Dr. Kaup :
(PI. 138, fig. 1). The normal incisive formula is;—g = 8: the
median pair being the largest above and the smallest below : in the
existing species the smaller incisors are disproportionally minute, and
usually have no permanent successors, or are soon shed ; the larger
incisors are preceded by deciduous teeth which they succeed and
replace. In the under jaw of a Sumatran Rhinoceros, now before me,
the extremity of which is figured in Plate 138, fig. 15, the tips of
the large permanent outer pair of incisors (i 2) are visible, but have
not pushed out their deciduous predecessors (d 2) ; and the sockets
(d 1) of those of the two small median incisors (i 1) are also retained.
In one of the extinct species of Rhinoceros from the Himalayan
tertiary beds Dr. Falconer informs me that there are six incisors in
both jaws : the typical number was, therefore, retained in this
ancient species, as in the contemporary Hippopotamus of the same
formations. Cuvier believed that the ex-incisive character of the
two-horned Rhinoceros of Africa was absolute. “ Not only,” he
observes, “ is its hide without folds, not only has it constantly two
horns, but it has never more than twenty-eight teeth, all molars ;
and never possesses incisors, nor even a place for them at the
anterior extremity of its jaws.”(l)
affording extra support to the horn-bearing bones of the face whence the name tichorhinus
given by Cuvier to this most common of the extinct Rhinoceroses of our Northern Hemisphere.
(1) “ Non-seulement sa peau n’a point de plis ; non-seulement il a constamment deux
cornes, mais il n’a jamais que vingt-huit dents, toutes molaires ; il manque toujours d’incisives,
et n’a même point de place pour elles à l’extremité antérieure de ses mâchoires.” * Ossemens
Fossiles/ 4to. 1822, tom. ii. pt. 1, p. 27. The otherwise excellent zoological descriptions of the
two-horned Rhinoceroses in Dr. Smith’s ‘ Illustrations of the Zoology of South Africa, do not