In the brown upper pharyngeal tooth of the carp, Stromeyer(l) I
detected a small proportion of magnesia.
8. Structure.—The tubular structure common to the dentine of I
all classes of animals, though not first discovered in the teeth of I
fishes, has been most frequently recognised, because most conspicuous, I
in them: and, as in several fishes, the coarser features of this I
structure are obvious to the naked eye, it was admitted as applicable I
to a greater or less proportion of that class by some comparative I
anatomists, before the researches of Purkinje and Retzius had established I
its existence in the teeth of the higher vertebrate animals. Leeuwen- I
hoek, indeed, in his account of the minutely tubular structure of the I
teeth of man and of the ox, (2) attributes the same structure to the I
tooth of the haddock, in which he states that the dental tubes are smaller I
than in the ox. Mr. André(3) detected the ramified canals which a
pervade the substance of the tooth of the Acanthurus. Cuvier (4) first I
described the coarser tubes composing the teeth of the rays and of I
the wolf-fish ; and Von Born (5) ascribes to the teeth of a greater I
number and variety of fishes the same structure, which was regarded I
by both these anatomists as analogous to the tubular structure of the I
teeth of the ornithorhynchus and orycteropus, and also compared with I
that of whalebone and of the horn of the rhinoceros. Such comparisons, I
however, are wanting in accuracy when applied in that loose and I
general manner.
In the following pages there will he shown to he, at least, I
four principal modifications of the tubular structure in the teeth I
of fishes. Premising that the essential character of this structure I
is a cavitas pulpi, or medullary canal, from which the calcigerous I
tubes radiate, the first modification which may be noticed is I
where the tooth is traversed by a number of equidistant and I
parallel medullary canals, each canal and its system of medul- I
lary tubes representing a cylindrical or prismatic denticle, and being I
separated from the contiguous denticles by a thin coat of bone or I
cement. This modification is exemplified in the rostral teeth of I
(1) Gilbert’s Annalen, Bd. vii, 1811.
(2) Philos. Trans., 1678, p. 1003.
(3) lb. vol. 74, Description of the teeth of Chætodon (Acanthurus) nigricans.
(4) Leçons d’Anat. Comparée, tome iii, p. 113 (1805).
(5) Heusinger’s Zeitschrift, Bd. i, 1827.
the saw-fish, (PristisJ, the tesselated teeth of the eagle-rays, (Mylio-
bates, Zygobâtes, Sfc.), and the maxillary plates of the chimæ-
roids. The dense dental case of the jaws of the parrot-fishes,
(Scarus), may likewise be regarded as an extreme instance of
this modification, and we shall find the same structure re-ap-
pearing in some of the inferior genera of the mammiferous class.
In the parrot-fishes, the denticles are quite distinct from one
another, hut in the saw-fish, chimæra, and eagle-rays, the contiguous
medullary canals occasionally anastomose together. In the chimæ-
roid fishes these anastomoses are more numerous, and the boundaries
of the component denticles less distinct, so that they form a
transition between the preceding, and what may be regarded as the
second variety of the tubular structure.
In this modification, the substance of the tooth is traversed by
medullary canals, somewhat less regularly equidistant and less
parallel than in the first ; having the boundaries of their respective
systems of radiated calcigerous tubes indicated by the minute
calcigerous cells, with which the terminal branches of those tubes
communicate ; these boundaries being more or less obscured by
the terminal branches of the calcigerous tubes extending across
into the interspaces of the corresponding branches of an adjoining
system of tubes, and anastomosing with them immediately, or
through intervening dilatations or cells. The medullary canals
here dichotomize more frequently than in the first modification ;
their anastomoses are more numerous, and the whole tooth, which
is generally of large size, is consequently more individualized and
compacted. The teeth of the Port-Jackson shark (Cestracion Phillippi,)
afford a good example of this modification, which also prevails in
those of the extinct genera Ptychodus, Psammodus, " Helodus, Ctenop-
tychius, 8fc. In the teeth of the extinct Acrodus, the medullary
canals, which likewise traverse in great numbers the body of the
tooth, assume a more or less wavy course ; and this disposition,
combined with their numerous anastomoses, leads to the third modification,
which at the same time is the most common and characteristic
of the dental structure, in the class of fishes.
In teeth manifesting this variety of the tubular structure, the
dentine is permeated by a network of medullary canals, of which the