PISCES. 
Teeth of the Tench. 
a, roof of the mouth ; b, the esophagus; c, dental 
projection from basilar bone ; d, d, pharyngeal teeth. 
(After Owen.) 
In the Cyprinide, or Carp-ge- 
nus, the bones composing the 
superior and inferior maxille are 
completely edentulous, but to 
make up for this deficiency the 
pharyngeal bones are armed with 
a remarkably powerful dental ap- 
a of very singular character. 
h of the inferior pharyngeal 
bones, which are exceedingly 
strong and form a kind of osseous 
framework at the commencement 
of the esophagus, supports four or 
five large teeth of great strength. 
These are opposed to a single 
dental piece of stony hardness and 
laminated structure, which is fixed 
979 
514), and thus forms a kind of anvil upon 
which the bruising pharyngeal teeth play, and 
thus crush and triturate whatever food passes 
into the esophagus. 
In the Scari, which have to feed upon the 
numerous corallines that clothe the rocks at 
the bottom of the ocean, the dental apparatus 
given to protect their jaws from injury while 
biting such hard substances is very remarkable. 
These Fishes have their jaws, which resemble 
the beak of a parrot (whence they receive their 
usual appellation “ Parrot-fishes,”) covered 
externally with a kind of pavement of teeth 
answering the same purpose as the horny 
investment of the mandibles of the bird. The 
teeth that form this pavement are perpetually 
in progress of developement towards the base 
of the jaw, whence they advance forwards, 
when completed, to replace those which become 
Fig. 516. 
Section of the jaw of the Parrot-fish, shewing the progress of dentition. 
c, teeth still enclosed in the jaw; 1, do. with their extremities 
upon a dilated projection from the protruded so as to form an external pavement. (After Owen.) 
basilar bone of the cranium (fig. 
Fig. 515. 
Beak of Parrot-fish ( Scarus muricatus ). 
@, upper mandible, the exterior of which is com- 
pletely encased in teeth; 5, lower mandible par- 
ially so, the inferior teeth not having as yet pro- 
truded ; ¢, lateral fangs. (After Owen.) 
worn away in front by the constant attrition to 
which they are subjected. 
In the annexed figure (fig. 515) the ex- 
ternal appearance of these singularly disposed 
teeth is well represented, while in the vertical 
section (fig. 516) the mode of their implan- 
tation into the anterior surface of the jaw is 
delineated. All these teeth were originally 
developed in a common alveolar cavity (516, c) 
situated in the substance of the jaw. The 
outer* wall of this cavity is much weaker 
than the dense and compact inner wall, and 
moreover it becomes thinner as it approaches 
D the margin of the jaws and disappears (fig. 
516, /,) at different distances in different spe- 
cies of Scari before it reaches that margin. 
Where it exists at the base of the jaws it is 
sometimes, as in Scarus muricatus represented 
in the figure, perforated by numerous small 
foramina, through which foramina in the recent 
fish processes of the external periosteum are 
continued to the analogous membrane lining 
the dentigerous cavity and forming the capsule 
of each denticle. These processes are analo- 
gous to the gubernacula of the second series of 
teeth in the Mammalia, and like them serve 
to conduct the new teeth to the exterior of the 
jaw. The growing denticles (516, /,) be- 
* Owen, Odontography, page 115. 
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