characters of classification, is much greater than in Reptiles or
Fishes, as will be seen in Part III. Yet there is a difference in this
respect in the different Orders, and the Dental System of the
Cetacea and Bruta has a much greater range of variation, and a less,
constant relation to the other characters on which the families and:
genera are founded, than in the Ungulate and higher Unguiculate
Species. But, with respect to these also, the value of the teeth
as zoological characters has been overrated.(l)
It is true, indeed, that the most manifestly natural Mammalian
genera are those, the species of which are provided with absolutely
similar molar teeth : and, that those genera, which include species with
molars of different forms, do not present the same character of unity.
But it does not follow that, by combining species of Mammals with
similar molars, a group will he formed perfectly analogous to those
which may be considered as the most natural or perfect. Neither the
molar teeth, nor any other solitary character will serve to establish a
natural classification.
The molar teeth will least mislead in this respect where their
modification is most extreme, as when they are adapted to divide the
flesh of animals, in which case they must of necessity be associated
with the faculties and instruments for seizing and destroying prey.
But molar teeth may be similarly modified, and equally well adapted
for crushing vegetable substances, which substances may be
sought for by one species on the dry land, by a second in 1
(1) M. F. Cuvier says “ Cette recherche me fit reconnaître que tous les genres manifestement
naturels, et admis comme tels par tous les naturalistes, étaient formés d’espèces pourvues
de machelières absolument semblables; que ceux qui comprenaient des espèces dont les
mâchelières différait, n’ offraient point ce caractère d’unité qui était le partage des premières ; et,
enfin, qu’en réunissant les espèces à mâcbebères semblables on reformait des groupes parfaitement
analogues à ceux que l’on pouvait considérer comme les plus parfaits.” Dents de Mammifères,
8vo. 1825, p. ix.
marshes, and by a third in the sea, or on the banks of rivers.
The grinding surface of the molar tooth, for example, may for
this purpose be elevated into a pair of transverse ridges, and
we find such molars in the Kangaroo, the Tapir, and the Manatee,
as also in the extinct Diprotodon, Nototherium, and Dinothérium.
The small anterior molars of the Mastodon giganteus
likewise present this form. It would be difficult to select from
the Mammalian Class the constituents of a more heterogeneous
group than would be constituted by the character which M.
F. Cuvier has assigned as the true guide to the formation of
the most natural and uniform genera in Mammalogy.
Even in regard to teeth adapted to carnivorous habits, were
these characters to form the sole guides in classification, species
of placental Mammalia would be associated with those of the
ovoviviparous sub-class ; and M. F. Cuvier, in illustrating his
generalization, observes : “ Les sarigues, les péramèles, et les
dasyures se sont réunis aux Insectivores, &c., &c., et je crois
avoir été conduit à ces modifications par des motifs légitimes.” (1)
The class of tissues in which teeth should rank, has frequently
been a subject of controversy in Systems of Histology ;
the fact being overlooked that they have not the same unity of
composition as bones or epidermal appendages. One constituent
of teeth, viz., the cement, unquestionably ought to rank with the
osseous tissue ; and the dentine, or ivory, which was described
for the last time in this country, in July, 1838, as being “ like the
hair, arranged in concentric layers,” (2) bears, on the contrary, a close
(1) Loc. cit. p. xi.
(2) Medico-chirurgical Review, p. 43. In France the dentine continued to be described,
as late as the end of 1839, as “ compose de cones lamelleux extrêmement minces, s’emboîtant
les unes les autres, &c.” De Blainville, ‘ Ostéographie’ Fascicule premier, Primates, p. 14, 1839.