usual position of the jaws in the osseous fishes. In consequence also
of the greater extent of ossification in these parts, the indications of
the separation of the upper jaw into maxillary and premaxillary, and
of the lower jaw into mandibular and premandibular pieces begin to
he visible. The upper jaw, besides being suspended to the tympanic
or articular pedicle, is articulated by a distinct convex process with
a corresponding concavity on each side of the vomerine portion of
the cranium. A similar connection of the upper maxillary hone,
in the Scarus, illustrates the analogy here advanced between the upper
dentigerous arch in the Cestracion and other Plagiostomes and the
ordinary maxillary and intermaxillary hones. This arch is also
attached by ligamentous matter, as in other sharks, to the frontal and
nasal parts of the cranium, with which it is in contact. The maxillary
portion of the upper jaw sends outwards a strong process which
is connected with a corresponding external process of the lower jaw,
and a very strong ligament attaches the inner side of the posterior
extremity of the superior maxillary bone to the inner side of the
broad transverse condyloid extremity of the lower jaw. The interspace
of the upper maxillary bones is occupied by a thin triangular
plate of cartilage representing the matrix in which, in osseous fishes, the
palatine hones are developed, and two lateral posterior processes of this
cartilage which abut against the tympanic pedicle, represent the transverse
and pterygoid bones.
The labial cartilages, regarded by Cuvier in the Squatina and
some other Plagiostomes as the rudimental and toothless representatives
of the maxillary, intermaxillary, and premandibular hones,
and which in the Cestracion might have been expected, in harmony
with the general tendency of its cranial structure, to have been
present with a corresponding advance towards their hypothetical
maxillary character, have, on the contrary, totally disappeared.
The lower jaw, consisting of the articular and premandibular
elements still confluent, is suspended partly to the slender tympanic
pedicle, but principally to the expanded posterior extremity of the
superior maxillary bone. It closely resembles the upper jaw in form,
but is of greater depth, and the symphysis, which is never obliterated,
is of greater breadth, and is terminated more squarely.
The teeth are arranged, as in the Plagiostomes generally, in
several antero-posterior rows, along the margin and inner surface of
both jaws ; but the rows are more oblique than in the sharks,
although less so than in certain rays, as Rhina; and the teeth present
greater diversity both of form and size, than in any other
existing plagiostome. The teeth of the upper jaw are delineated in
fig. 2, PI. 11.
The teeth at the anterior part of the jaws are the smallest;
they present a transverse, sub-compressed, conical figure, with the
apex produced into a sharp point; these points are worn away from
the used teeth at the anterior and outer parts of the jaw, but are
strongly marked in those which still lie below the margin. There are
six subvertical rows of these small cuspidate teeth on each side
of the jaw, together with a median row close to the symphyseal line ;
and from twelve to fourteen teeth in a row. Behind the cuspidate
teeth, the five consecutive rows of teeth progressively increase in all
their dimensions, but principally in their antero-posterior extent;
the sharp-point is converted into a longitudinal ridge, traversing
a convex crushing surface; and the ridge itself disappears in the
largest teeth. As the teeth increase in size, they diminish in number,
in each row ; the series of the largest teeth includes from six to
seven in the upper, and from seven to eight in the lower jaw.
Behind this row, the teeth, although preserving their form as
crushing instruments, progressively diminish in size; while at the
same time, the number composing each row decreases. From
the oblique and apparently spiral disposition of the rows of
teeth, their symmetrical arrangement on the opposite sides of the
jaw, and their graduated diversity of form, they constitute the most elegant
tesselated covering of the jaws which is to be met with in the
whole class of fishes.
The modifications of the form of the teeth above described,
by which the anterior ones are adapted for seizing and retaining,
and the posterior for cracking and crushing alimentary substances,
we shall find to be frequently repeated with various modifications
and under different conditions in the osseous fishes. They
indicate, in the present species, a diet of a lower organized character
than in the true sharks, and a corresponding difference of habit and
e 2