the five outer ones are the largest and have the triturating surface
very elegantly dentated.
The bream (Brama) has five pharyngeal teeth in a single row on
each side; they are moderately large, compressed and obliquely
bevelled to a cutting edge, which works against the occipital tooth
above. The teeth of the tench (Tinea) are similar to, but relatively
broader than those of the bream: their oblique triturating surface
is produced internally into a slightly hooked point, as represented
in PI. 57, fig. 5 ; they are arranged in a single row, four or five on
each side of the pharynx, and work against a thick and dense triangular
superior pharyngeal plate (a) imbedded in the basi-occipital
bone. Similar pharyngeal teeth have been found to characterize two
extinct species of tench, viz. Tinea leptosoma and micropygoptera,
Agass.
Both the tench and carp combine a large proportion of vegetable
matter, derived from aquatic plants, with worms and the larvae of insects,
for their ordinary food ; hut the carp, (Oyprinus Carpio), from
the nature of its dentition ought to be the most herbivorous species
of the family- In this species, the pharyngeal teeth are arranged in
two or three rows ; the innermost represented by a single tooth, the
second having sometimes two teeth of larger size ; and the outer row
including three or four, which are the largest and most complicated,
especially the middle one. The anterior and inferior tooth of this row
has a round crown, with the centre raised into a small point; the
rest are terminated by a flattened grinding surface, sculptured with
transverse undulating furrows. These are not very deep, so that
they disappear, as shown in PL 57, fig. 6, when the tooth is moderately
worn down. Fig. 7, exhibits the grinding surface on a
tooth recently anchylosed to the pharyngeal hone, and fig. 8 shows
the inferior surface of the furrowed crown of an incompletely formed
tooth as seen on looking into the wide and open pulp-cavity. The
incudeal triangular dental plate, implanted in the occipital bone, is
extremely dense, and presents a clear transparent amber-colour in the
carp as in the tench • hut its contour is more equilateral in the carp,
and the surface which receives the appulse and friction of the pharyngeal
molars is flatter.
It is sufficiently obvious from an inspection of the powerful
muscles which work the pharyngeal bones, that the teeth, whether
adapted for piercing or lacerating aquatic animals, or for triturating
vegetable substances, must be used with such force as soon to be rendered
unserviceable, and to require renewal. I had formerly made
sections of the dried pharyngeal bones of our common Cyprinoid
fishes, under this conviction, in quest of the hidden germs of the
replacing teeth, but without success. A subsequent acquaintance
with the place of development of the successors to the maxillary teeth
in certain fishes, as already described in the pike, alepisaur, &c., led
me to renew the search in the substance of the thick and soft mucous,
membrane of the pharynx surrounding the pharyngeal hones, and,
I soon detected the germs of the successional teeth in this situation. (1}
The primitive papilla first developed from the surface very soon,
sinks into the substance of the mucous membrane, and becomes
inclosed by a complete capsule. I have not been able to detect in
the carp or tench an enamel-pulp developed from the surface of the
capsule covering the crown of the contained tooth: this adheres only
to the dentinal pulp, and by means of its base to a part of the circumference
of the capsule. The hollow cap of dentine of a half-formed tooth
is easily displaced from the formative pulp in consequence of its dense:
structure presently to be described | but the surface so exposed when
viewed by a strong reflected light, with a \ inch focus, is clearly seen
to be an artificial and lacerated surface : it is minutely honey-combed,,
by the rupture of the calcified from the uncalcified portions of the
nascent calcigerous tubes ; and the subjacent and still unconfluent
cells, are seen torn from the substance of the pulp, and scattered irregularly
over its surface. When the pulp of the crown of the tooth is
completely calcified, the margin of its base begins to assume a ligamentous
density, and attaches itself to the margin of the pharyngeal
bone, near the base of the tooth about to he displaced. I have not
observed any further stage in the singular process of transference of
the loosely imbedded tooth from its mucous capsule to the bone with
which it is destined to form a common and continuous part.
In this process of union, which is analogous to that of the separated
portions of a fractured bone, the question suggests itself, by what
(1) See PI. 57, fig 6, in which a young tooth c is exposed by a reflection of part of its
mucous capsule, b.