of connexion between those parts, either as elastic ligaments, or by
continuous ossification.
Here we have the second step in the development of the mammalian
tooth represented, viz : the imbedding of the pulp in a follicle of the
mucous membrane; but the eruptive stage of the tooth takes place
without any previous inclosure of the follicle and pulp in the substance
of the jaw.
In the Balistes, Sparoids, Sphyreena, Scarus, and many other fishes,
the formation of the teeth presents all the usual stages which
have been observed to succeed each other in the dentition of the
highest organized animals j the papilla sinks into a follicle, becomes
surrounded with a capsule, and is then included in a closed alveolus
of the growing jaw, where the development of the tooth takes place,
and is followed by the usual eruptive stages.
The development of the dental pulp in fishes, prior to the deposition
of the calcareous particles in it, corresponds in the main with the
process described by Purkinje and Kaschkow in the mammalia. The
pulp-substance, or contents of the membrana propria remain, in fishes,
for a longer period in a fluid or semi-fluid state, and the granules or
nucleated cells which are first developed, float loosely or in small
aggregated groups in the sanguineo-serous fluid : they first attach
themselves to the inner surface of the membrana propria, if these be
not originally developed from that surface, and the whole of the contents
of the growing pulp becomes soon after condensed by the numerous
additional granules which are rapidly developed in it after it
has become permeated by the capillary vessels and nerves. The arrangement
of these particles into linear series, or fibres, is first observable
at the superficies of the pulp to which the fibres are vertical \
and, at this period, ossification has commenced in the dense and
smooth membrana propria of the pulp : it is thence continued centri-
petally in the course of the above-mentioned lines, towards the base
of the pulp, either regularly progressive, as in the incisors of the
Sargus and Balistes, or radiating, as in Sphyrana and (if we may judge
by a posteriori observation of the structure of the fully developed teeth)
in most other fishes, from the various centres formed by the persistent
capillaries of the pulp, around which the cells or granules become
I condensed into concentric layers, which then become, as they are
I successively impregnated with the calcareous salts, the walls of the
I medullary canals. (1.)
In the shark, and all those fishes in which the teeth are completely
I formed without going beyond the papillary stage of development, there
lis no distinct enamel-pulp ; the dense exterior layer of the tooth is
■ formed by the calcification of the ‘ membrana propria’ of the pulp,
■ which, therefore, precedes the formation of the ordinary dentine. But
Jin the file-fish fBalistesJ, the sargus, the gilt-head (Chrysophrys), and
I some other fishes, a conspicuous enamel-pulp is developed from the
inner surface of the capsule which surrounds the bone-pulp : this enamel
»organ terminates, as in the human subject, before the capsule is re-
jflected upon the base of the pulp. It has a firmer tissue, more
■ closely resembling that of the ordinary pulp, than in the mammalia :
land, when examined under the microscope, presents numerous and
■ close-set fine fibres near that surface which is next the bone-pulp,
land to which these fibres are generally placed at right angles. The
Jbase of the enamel organ, which is attached to the capsule, presents
la granular and fibrous tissue blended together. I have not been able
to trace any capillaries from the capsule into the substance of the
■ (1) In those fishes, and they include the greatest part of the class, in which the teeth are attached
by anchylosis to the jaws, the mode in which the calcareous particles are deposited in the
■ gelatinous frame-work or pulp is modified as the calcification approaches more or less gradually
■ towards the base of the tooth, until at length the pattern or texture of the calcified pulp cannot
fbe distinguished from that of the bone with which it thus becomes continuous. It is not with-
|out interest to observe how Cuvier, who had clearly dëtected this actual ossification of the base
jlof the pulp in the teeth of many fishes and reptiles, should have conceived it to be a process so
■ distinct from that peculiar to the supposed inorganic tooth, that he felt himself called upon to
■ correct the error he had fallen into in stating, in his “ Leçons d’Anatomie Comparée.” this
■ ossified base of the anchylosed tooth to be its root. Describing the teeth of lizards, in his “ Osse-
Imens Fossiles,” tom. V, 2e partie, p. 274, Cuvier says :—“ Cette base ne se divise point
Jen racines ; mais quand la dent a pris son accroissement, il arrive le même phénomène que
Bans les poissons. Le noyau gélatineux s’ossifie; il s’unit intimement d’une part, à l’os
Ha la mâchoire, en contractant, de l’autre, une adhérence intime avec la dent qu’il a
^exsudée.—J’avais déjà exposé l’histoire de cette dentition dans mes Leçons d’Anatomie
■ Comparée, III. iii. 113, etc.; mais j’y ai aussi commis l’erreur d’appeler racine cette partie cellu-
Huse et osseuse qui s’unit à l’os maxillaire.” The application of the microscope to the investiga-
■ jon of the structure of the teeth has brought to light many instances in which the crown of
■ be tooth ought, for the same reasons, to have as little title to be considered a part of the tooth
the root.
C