PISCES. 
that of their teeth and bones, as will be evident 
from the following analysis made by M. Che- 
vreul of the scales of a Lepidosteus, of a Cheto- 
don, and of the Perca labrax, after they had 
been thoroughly dried by exposure during six 
weeks to a dry atmosphere. In drying, the 
scales of Lepidosteus lost 11.75 per cent., of 
Chetodon 13 per cent., and those of the Perca 
labrax 16 per cent. 
Scales of 
Lepi- | Perca | Cheto- 
dosteus| labrax.| don. 
Fatty matter principally con- 
sisting of oleine . . ~.{ 0.40] 0.40) 1.00 
Azotized matter . . . «| 41.10) 55.0 | 51.42 
Chloride of sodium . . .| 00.10) Trace] Trace. 
Sulphate of soda. . «| 00.10} 00.90) * 1.00 
Subcarbonate of soda . .| 00.10} 00.00} ' 0.00 
Subcarbonate of lime . .{| 10.00} 3.06] 3.68 
Phosphate of lime (of bone) | 46.20] 37.80} 42.00 
Phosphate of magnesia. .| 2.20] 0.90} 0.90 
Peroxide of iron . - . . | Trace|Trace| Trace 
WOOBB Nits “eo “ens % % 0.00) 2.84 a 
100.00} 100.00} 100.00 
In a preceding article (see Osszous System, 
Comp. Anat.) we have endeavoured to shew 
that the scales which invest the exterior of the 
body constituting the exoskeleton of Fishes, 
by progressive modifications in their size, tex- 
ture, and arrangement, are converted into very 
various organs, namely, the apparently osseous 
plates that cover Lepidosteus and Ostracion, 
the formidable pieklce that stud the external 
surface of the Diodons, the opercular flaps of 
the Sturgeon, and even those of the osseous 
Fishes; the spines of Gasterosteus, and those 
which in Silurus, Ba- 
listes, and Lophius, 
were likewise proved 
to belong to the epi- 
dermic or tegumen- 
tary system; lastly, 
the fin-rays and in- 
terspinous bones of 
the vertical fins were 
found to be derivations 
from the exoskeleton, 
instead of being, as 
they have long been 
considered, parts ap- 
pertaining to the en- 
doskeleton or true 
Osseous system. . 
The dental organs 
-of vertebrate animals 
have very naturally 
been regarded by the 
old anatomists who 
confined their osteolo- 
gical researches to the 
investigation of the 
human skeleton, as 
forming a part of the 
bony framework of the 
body, notwithstand- 
ing that the teeth in 
every particular of their economy were con- 
fessedly very different from any other pieces 
of the skeleton. 
975 
Any one who with a little care examines the 
dental apparatus of Fishes will, however, 
speedily be convinced that the teeth in common 
with the epidermic structures above enumerated 
are all of cuticular origin, their connection with 
the real osseous skeleton, by their roots be- 
coming consolidated with certain bones of the 
mouth or implanted into the jaws, being by no 
means an essential or even constant circum- 
stance. 
Every one knows that the skin covering the 
body of the Skate or Thornback is thickly studded 
with calcareous spines, some of microscopic 
size, but others of considerable dimensions. 
On tracing these cuticular spines towards the 
mouth they are found, as they pass over the 
manducatory surfaces of the upper and lower 
jaws, to become suddenly very much increased 
in size, and are arranged with such regularity 
that they constitute a very formidable set of 
dental organs, consisting of ten or a dozen rows 
of sharp teeth, which answer every purpose con- 
nected with the seizing and swallowing of food. 
These teeth, however, or scales, for such they 
indubitably are, have no connection with the 
jaws that support them except through the in- 
termedium of the cutis or mucous membrane 
covering the mouth, from which they are deve- 
loped, and are continually in these Plagiostome 
genera in progress of formation behind as they 
are worn away in front, their developement 
being accomplished in the following manner.* 
A series of minute and closely aggregated pa- 
pilliform matrices or pulps rise in succession 
from the mucous membrane behind the teeth 
already formed, which gradually become ossi- 
fied by the deposition of calcareous salts in the 
Fig. 509. 
Skull and jaws of Port Jackson Shark ( Cestracion Philippii), shewing the forms 
and arrangement of the teeth. 
peripheral cells and radiating tubes of which 
the pulp consists. 
* Owen, Odontography, 4to. 1840. 
