the island of the anterior lobe (e)—presents a small accessory
fold at the inner side of its posterior horn: in the posterior
lobe the fold is represented by a small circular island of enamel (e-)
both are soon obliterated as the tooth wears down. There is an
accessory column at the internal interspace of the lobes in Alces
as in Megaceros, which is not present in the Rein-deer or Fallow-
deer, hut it is rudimental and confined to the base of the fissure.
The anterior border of the outer concavity of each lobe is unusually
produced.
In the Giraffe (fig. 7) the median convexity of the outer
surface of the anterior lobe (o) is more prominent than the
anterior border of the depression from which it rises, whilst
the anterior border of the posterior lobe (o’) is more produced
than the middle prominence : this distinctive character is well
shown in the upper molars of the fossil Giraffe from the Sewalik
Hills, noticed by Captain Cautley in the ‘ Journal of the Asiatic
Society of Bengal,’ Vol. v i i , pp. 658-660, and figured in
his joint communication with Dr. Falconer, in the ‘ Proceedings
of the Geological Society,’ No. 98, PI. 2, fig. 3 & 4; the last
and penultimate molars are specifically distinguished by an obtuse
lobe at the bottom of the outer interspace of the two lobes.
The crescentic enamel folds are continued into each other until
the tooth is worn low down; hut their outer boundaries are earlier
completed than in the E lk: the two principal lobes are divided
almost to the base of the crown: the internal column is reduced
to a very small basal rudiment. The enamel of the Giraffe’s
molars is unusually rugose and resembles that of the Sivatherium.
The molars of the Camel (fig. 8), present the most simple condition
of the ruminant type of these teeth : the transverse fold
dividing the crown being short, the dentine of the two lobes forms a
continuous tract: the common base of the crescentic vertical folds
of the capsule being likewise short, the enamel islands are soon
separated from each other: they include a shallow or narrow
crescentic cavity, with a simple but slightly sinuous contour. The
two outer shallow longitudinal depressions of the crown (o o-) have no
middle rising; and there is no columnar process at the interspace;
of the two inner convexities. Bojanus has well illustrated these
characteristics of the upper molars of the Camel in his Memoir on
the Merycotherium{\), a large extinct Cameloid genus of Ruminants
founded on fossil remains discovered in Siberia, and he has extended
the comparison to the Sheep, the Elk, and the Ox.
Cuvier compares the lower molars of the Ruminants to the upper
ones reversed: in the lower true molars the single median longitudinal
fold is external and divides the convex outer sides of the two
lobes (fig 3-, o o): the base of the fold extends in some species across
the molar for some depth, before it contracts towards the outer side,
and the two lobes of the crown accordingly continue to be completely
divided for a longer period, as in the Elk and Giraffe
(figs. 6 & 7): the inner surface of the molar is gently sinuous,
the concavities being rarely so deep as those of the outer surface
of the upper molars : the lower molars are always thinner in
proportion to their breadth than those above, and the crescentic
islands are narrower and less bowed. The differences which the
lower molars present in different genera of Ruminants are analogous
to those in the upper molars, but are less marked | the accessory
small column when present, as in Bos, Urus, Megaceros and Alces, is
situated at the outer interspace of the convex lobes, and nearer the
base in the Cervidce than in the Bovidce: in the Giraffe it is present
in the first, but not in the second or third true molars ; it is not
developed in the Antelopes, Sheep or Camel, and is wanting in most
of the smaller species of Deer : other differences are expressed m
Plate 134. The last true molar of the lower jaw is characterised in
all Ruminants by the addition of a third posterior lobe : this is very
small and simple in the Camel and the Gnu, is relatively larger in
the Bovidce and Cervidce, presents in the Megaceros and Sivatherium(2)
a deeper central enamel island or fold, which also characterises the
(1) Nova Acta Nat. Curios. 4to. 1824, tom. xii, pt. i, p. 265, tab. xxi.
(2) The last lower molar of this most gigantic of Ruminants is figured in PI. 133,
fig. 3. Cuvier (loc. cit. p. 5) describes the two lobes of the lower molars as being composed
of two half-cylinders forming crescentic ridges on the grinding surface, and the last lower
molar as having an additional half cylinder, and consequently a grinding surface of five
crescents : the crescentic ridges are formed by the vertical descending fold, which divides the
summit of the lobe, and the fact is that the third lobe of the last molar has also this fold; but
it is shallower and the entire lobes are smaller. In most Ruminants the crescentic enamel island
or fold is therefore soon obliterated in the third lobe; but in some species it is deeper and