present examples of teeth developed in the median line of the mouth,
as in the palate of the myxines, or crossing the symphysis of the
lower jaw, as in the scymnus and myliobates.
5 .Attachment.—The teeth of fishes present greater diversity in their
mode, as well as place of attachment, than is observable in those of any
other class of animals. In a few instances, they are implanted in sockets,
to which they are attached only by the surrounding soft parts, as
e. g., the rostral teeth of the saw-fish. (1) Some have their hollow base
supported, like the claws of the feline tribe, upon bony prominences,
which' rise from the base of the socket; the incisors of the file-fish
afford this curious example of a double gomphosis, the jaw and the
tooth reciprocally receiving and being received by each other. (2)
The teeth of the Sphyrcena, Acanthurus, Dictyodus, &c., are examples
of the ordinary implantation in sockets, with the addition of a slight
anchylosis of the base of the fully-formed tooth with the parietes of the
alveolar cavity. But by far the most common mode of attachment of the
fully-formed teeth in the present class, is by a continuous ossification
between the dental pulp and the jaw; the transition being gradual
from the structure of the tooth to that of the bone: the tooth,
prior to the completion of the anchylosis, is connected by ligamentous
substance,ieither to a plain surface, an eminence, or a shallow depression
in the jaw-bone.
Sometimes not the end, but one side of the base of the tooth is
attached by anchylosis to the alveolar border of the jaw ; it might be
supposed that, in this case, the crown of the teeth in both jaws
would project forwards instead of being opposed to one another,
and such, in fact, must have been their position were it not that, in
some instances, as in the Pimelipterus, the teeth have the crown
bent down at nearly a right angle with the base. In the scarus,
and likewise in the marginal teeth of the diodon, where the teeth
are straight, and attached horizontally to the margin of the jaws,
their sides instead of their crowns are actually opposed to one another.
In the cod-fish, wolf-fish, and some other species, m proportion
as the ossification of the tooth advances towards its base and
along the connecting ligamentous substance, the subjacent portion
of the jaw-bone receives a stimulus, and developes a process corres-
(2) PI. 40, figs. 3 and 5, a.
ponding in size and form with the solidified base of the tooth. In
this case, the inequalities of the opposed surfaces of the tooth and
maxillary dental process fit into each other, and for some time
they are firmly attached together by a thin layer of ligamentous
substance ; but in general, anchylosis takes place to a greater or less
extent before the tooth is shed. The small anterior maxillary teeth of
the angler (Lophius) are thus attached to the jaw, but the large posterior
ones remain always moveably connected by highly elastic, glistening
ligaments which pass from the inner side of the base of the tooth to
the jaw-hone. These ligaments do not permit the tooth to be bent
outwards beyond the vertical position, when the hollow base of
the tooth rests upon a circular ridge growing from the alveolar
margin of the jaw ; but the ligaments yield to pressure upon the tooth
in the contrary direction, and its point may thus be directed towards
the back of the mouth ; the instant, however, that the pressure is remitted,
the tooth flies back, as by the action of a spring, into its usual
erect position; the deglutition of the prey of this voracious fish is
thus facilitated, and its escape prevented. The broad and generally
bifurcate osseous base of the teeth of sharks is attached by ligaments
to the ossified or semi-ossified crust of the cartilaginous jaws. The teeth
of the Salarias and of certain Mugiloids are simply attached to the gum.
The small and closely-crowded teeth of the rays are also connected by
ligaments to the subjacent maxillary membrane. The broad tesselated
teeth of the eagle-rays have their attached surface longitudinally
grooved, to afford them better holdfast; and the sides of the contiguous
teeth are articulated together by true serrated, or finely-undulating
sutures ; which mode of fixation of the dental apparatus is unique in
the animal kingdom.
If the engineer would study the model of a dome of unusual
strength, and so supported as to relieve from its pressure the floor
of a vaulted chamber beneath, let him make a vertical section of one
of the crushing pharyngeal teeth of the wrasse. (1) The base of this
tooth is slightly contracted, and is implanted in a shallow, circular
cavity, the rounded margin of which is adapted to a circular groove
in the contracted part of the base; the margin of the tooth, which
immediately transmits the pressure to the bone, is strengthened by an
(1) PI. 8, fig. 3. Cl) PL 46.