enamel-pulp. In the incisors of the sargus, the development of the j
enamel and dentine begins simultaneously upon the contiguous sur- s
faces, and when we observe how close and compact is the package I
of the matrix of the tooth in the alveolar cavity of the jaw, it is I
hardly possible to conceive how either of these substances could be I
the product of transudation from their respective pulps. It is, how-1
ever, easier to separate the primary layers of the enamel and dentine I
from their respective pulps than from each other ; yet if the denuded
surfaces of the uncalcified portions of the pulps be examined by reflected
light under a compound lens of a half-inch focus, they are seen
to be ragged and punctate, and evidently different from the original
surfaces prior to the commencement of the deposition of the calcareous I
salts in them. The formation of the enamel resembles more closely
that of the dentine in the fishes cited than it does in the mammalia,
and the enamel contains a greater proportion of 'persistent animal
matter.
The course of calcification of the two pulps takes opposite directions,
and in the balistes, the process finishes by the ossification of
the outer layer of the capsule itself, by which both the enamelledl
crown and the base of the tooth are coated with a thin layer of bone. I have not been able to discern any radiated cells in this analogue ofl
the “ crusta petrosa,” or cement of the mammalian teeth. It soon
wears off from the crown of the extruded tooth.
In all fishes, the teeth are shed and renewed, and this not once
only, as in most mammalia, but frequently and during the whole
life time of the animal. (1) Fishes, indeed, can hardly he said to have
permanent teeth. The rostral teeth of the pristis constitute, perhaps,
the sole exception ; and these may be regarded rather as modified
dermal spines.
In all cases where the first teeth are developed in alveolar cavities,
I General Introduction. But in the great majority of fishes, the germs of
I the new teeth are developed, like those of the old, from the free
■ mucous membrane of the mouth throughout the whole period of
■ succession, a condition which is peculiar to the present class. The
I angler, the pike, and many of our common fishes, illustrate this mode
■ of dental reproduction: it is very conspicuous in the cartilaginous
■ fishes, in which the entire phalanx of their numerous teeth is
■ ever moving slowly forward in rotatory progress over the alveolar
1 border of both upper and lower jaws, the teeth being succes-
■ sively cast off as they reach the outer margin, and new teeth rising
■ in equal proportion from the mucous membrane behind the rear rank
I of the phalanx.
the succeeding ones follow them in the vertical direction, and owe the
origin of their matrix to the continuation, from the mucous capsule of
their predecessors, of a cæcal process, in which the papillary rudim ent
of the dental pulp is developed according to the laws explained in the
(1) In a few cases it is observed, that as the fish gets old, some of the deciduous teeth are not
replaced ; in old Salmonidæ, the vomer thus becomes edentulous, or nearly so.
This endless succession of new and sometimes, as in Balistes, and
■ Saryws, of highly complicated matrices,—this constant development
■ of a new apparatus for the production of each new tooth, even where II its final development is unaccompanied by an eruptive stage, and
I where the destruction of any part of the formative apparatus is not
| a necessary consequence of the completion of the tooth, could
I hardly seem other than a waste of the formative energies to the J reflecting physiologist entertaining the doctrine of dental development
■ by transudation, and by whom the dental pulp must have been I
■ regarded in the capacity of a gland. The destruction or waste
Iof other glands by no means follows the natural exercise of their
functions: the disappearance of the pulp pari-passu with the
'growth of the tooth, is only an inevitable consequence when that ngrowth is effected by deposition of the calcareous particles in the
I substance, instead of by transudation from the surface of the formative
I I pulp, and when fresh material is not progressively added to the base of the pulp. In the cyclostomous fishes, where the albuminous,
I horn-like teeth seem really to be transuded from the pulp, these are
[persistent; and thé new teeth are formed immediately beneath the
I old, and from the same surface of the reproductive pulp.