C H A P T E R II.
T E E T H OF CY C L O S T O M E S .
MYXINES.
10. In the class of fishes, as in that of reptiles and mammalia, there
are species which are wholly destitute of teeth. These edentulous
fishes are most common in the cartilaginous division of the class.
The sand-prides (Ammocetes), the sturgeons (Acipenser) , the paddle-
fishes (Planirostra and Aodon), are examples. The whole order of
Lophobranchii of Cuvier, which includes the pipe-fishes (Syngnathus),
and the Hippocampus, is edentulous.
The lowest organized fishes with worm-like bodies and parasitic
habits, as the myxinoids and lampreys, are also destitute of true
calcified teeth, but have them replaced by horny substances of a
conical, sharp-pointed, and often slightly recurved form, resembling
the teeth of the entozoa, the habits of which these suctorious fishes
simulate. The hag-fish (Myxine glutinosa), and other cognate species
now grouped together by Müller under the genus Bdellostoma, have
a single tooth on the median fine of the palate, and a double serrated
horny plate on each side of the upper surface of the tongue. The
palatal tooth(l) is moderately long, conical, and recurved, with a tumid
margin around its base, which is hollow, and supported upon a conical
pulp, firmly attached to a fibro-cartilaginous plate, (2) situated beneath
the anterior commissure of the palatal cartilage. The basal-plate
of this tooth is further attached by ligaments, the anterior of which
passes to the hinder part of the rostral cartilage, and the posterior
one to a cavity at the commissure of the marginal palatal cartilage.
The lingual dental plates (3) are four in number, two on each side,
of a curved form, hollow at the base, and implanted, like the palatal
tooth, on a reproductive pulp of a corresponding form. (4) This pulp,
and the margin of the base of the dental plates are attached to the
perichondrium of the lingual cartilage. The dentations of these
lingual plates are conical, suh-compressed, sharp-pointed, with the
(1) PI. 2, fig. 1, 6. (2) ib. a. (3) ib. fig. 2, b. (4) ib. fig. 3, a.
I points reflected backwards. They are usually described as distinct
■ teeth, and, viewed as such, form two concentric curved lines inter-
I rupted at the middle of the tongue. In the Myxine glutinosa the I number of lingual teeth is jjljj, i. e., there are eight teeth in both the
I right and left anterior rows, while there are eight in the left posterior
■ row, and nine in the right posterior row. In the Bdellostoma hep- I tatrema, there are ®z! lingual teeth ; in Bdell. heterotrema, the number
lis nZii; in the Bdell. hexatrema, the lateral rows of lingual teeth are
I symmetrical, being }}z}l ; in Bdell. cirratum, there are jjZn teeth ;
lin Bdell. dombeyi, the number is “z“. These formulae appear to be
■ constant in the species ; this is, at least, the case in the glutinous
■ hag. The middle teeth are always the longest, the rest gradually
»diminish towards the lateral extremities of the rows.(l)
I have already alluded to the parasitic habits of these low
■ organized fishes. When they first attach themselves to their prey,
■ the single median recurved palatal tooth is thrust into its flesh, and
iserves as a holdfast,, while the work of destruction is carried on by
■ the laterally opposed lingual saws, aided by the suctorious action
fof the mouth. The usual situation in which the myxine is found,
ns the interior of a cod or other large fish, into whose carcase it has
fthus penetrated, and on whose soft parts it has preyed.
LAMPREYS.
11. In the lampreys fPetromyzonJ,(2) there are labial and inferior
^naxillary, as well as palatal and lingual teeth ; all these are likewise
liomy substances, of a simple, conical, sharp-pointed, form, and of a
somewhat less dense texture than in the myxinoids. They are
tiollow, and supported on conical, reproductive pulps. The pulps
pf the labial teeth are firmly attached by their base to the fibrous
tissue of the lining membrane of the lip.
The labial teeth of the outer or marginal circle are the smallest;
from these, the teeth increase in size as they approach the centre of
|he cavity of the mouth. The converging series in the mesial plane
|re arranged in a straight line ; those of the sides in curved lines,
with the concavity towards the lower margin of the mouth. In the
(1) See Müller, über den Myxinoiden, p. 20. (2) PI. 2, figs. 4 and 5.