4 FORM. SITUATION.
Aplodactylus, (fig. 10) ; in the lower maxillary teeth of the Boops,
the crown is divided into five lohes by a double notch on each side j of the middle and largest lobe, (fig. 11).
In the great barracuda-pike (Sphyrcena), the crown of both the I
large and small lamelliform teeth is produced into a sharp point, and
closely resembles a lancet, (PL 1, fig- 4, & PL 53). A similarly
shaped piercing and cutting tooth may be accompanied by one or
more accessory compressed cusps at its base, as in the teeth of certain
sharks, (Pl. 3 & 4,) or the margins of the crown may be variously
notched, serrate, e. g., as in the priodon, (Pl. 1, fig. 12,) and in the
teeth of the great sharks of the genus Garcharias, or crenate as in the |
genus, hence called Crenidens, (fig. 7,) and in the teeth of the Acan-
thuri, (Pl. 44,) of which the species called Ctenodon is remarkable for
the deeply crenated, expanded and spatulate crowns of its teeth, (PL
1, fig. 6). Prismatic teeth of three sides are present in the jaws
of the Myletes, where each angle of the coronal surface is produced
into a point. The small teeth with which the jaws of the Scarus are
paved are four sided prisms; the strong flat teeth which form the
tesselated pavement of the jaws of the Eagle-rays (Myliobates), present
beautifully regular hexagonal or pentagonal forms (Pl. 25).
4. Situation.—Before proceeding to consider the situation of
the teeth of fishes, a few words may he premised respecting the
bones which enter into the formation of the mouth in the ordinary
osseous species. In these, the upper margin of the mouth is
hounded generally by the intermaxillary bones alone, which extend
backwards from the middle line to the angles of the mouth; in
this case, the superior maxillary bones(l) run parallel with and above
the horizontal portion of the intermaxillari.es ; (2) but when, as m
the lophius and salmon-tribe, the intermaxillary hones do not
extend to the angles of the mouth, the osseous boundary is completed
above by the superior maxillaries.(3) The lower border of
the mouth is formed by the premandibular bones, (4) this name being
given to the anterior of the two pieces of which each ramus o
the lower jaw consists in fishes. The roof of the mouth is forme
anteriorly by three hones which extend backwards from the interspace
of the intermaxillary bones ; the two lateral ones are the pa-
(1) Pl. 41, b. (2) Pl. 41, 0. (3) Pl. 60, fig. 1, b. M P1- clatines,
(6 b Pl. 61), the median one is the vomer, (c Pl. 61). Two flattened
bones on each side, called the pterygoid and transverse bones,
complete the bony arch or buttress which extends from the intermaxillaries
to the pedicle supporting the lower jaw. Posteriorly, the
j roof of the mouth is completed by the sphenoid and sub-occipital bones.
The floor of the mouth is supported by the median longitudinal
[chain of lingual bones, to the sides of which are attached the inferior
extremities of the branchial arches ; these form the sides of the
posterior part of the mouth, which gradually contracts to the pharynx ;
I this orifice is strengthened by bones above and below, varying in
number from one to six, and called the pharyngeal bones.
In the roach, dace, barbel and most other cyprinoid fishes, the
teeth are limited to the pharyngeal hones ; in the carp, the upper
[pharyngeal dental plate is wedged into a cavity of the occipital hone.
In the ordinary sharks and rays, on the other hand, the teeth are
[confined to the maxillary cartilages bounding the anterior aperture
I I of the mouth. The wrasse, (Labrus), and parrot fish, (Scarus), are
| instances in which the intermaxillary and premandibular, as well as
the pharyngeal bones are provided with teeth, both the anterior and posterior apertures of the mouth being thus surrounded by instruments
for dividing or comminuting the food. In other fishes, we
find the teeth situated not only on the bones which bound the anterior
and posterior orifices of the mouth, but in the intermediate
‘positions, as on the palatines, the vomer, the lingual hones, or the
branchial arches ; sometimes, also, but more rarely, on the transverse,
or pterygoid, the sphenoid, (1)M and the superior maxillary hones, of
which latter situation the fishes of the Halecoid(2) tribe and the
[extinct Lepidotus, afford examples in the present class. Among
a the anomalous positions of teeth may be cited, in addition to the
| occipital alveolus of the carp, the accessory rostral cartilages, which
in the Pristis are elongated, and so ossified as to he adapted to retain
' in sockets the strong sharp lateral teeth, constituting its formidable
[saw. In the lampreys, and in one of the osseous fishes (Helostomus)
most of the teeth are attached to the lips. Lastly, I may observe,
that it is peculiar to the class of fishes among vertebral animals, to
(1) Pl. 48, fig. 2. (Sudis).
(2. In this family M. Agassiz includes the Salmonoid and Clupeoid fishes of Cuvier.