part of the tooth the calcigerous tubes describe their various inflections
in a plane transverse to the axis of the tooth ; but towards the apex they
begin gradually to rise from that plane ; and as the pulp-cavity reassumes,
with the tooth itself, the simple conical form beyond the
termination of the poison-canal, the calcigerous tubes extend to
equal distances from the linear remnant of the pulp-cavity, which has
again passed to the centre of the tooth, and those tubes which are
continued from its continued extremity, pass to the apex of the fang in
a line parallel with the axis of the tooth. The calcigerous tubes
present secondary curvatures of a slightly wavy character, which
ecome more marked and irregular near their termination. In
whatever part of the section an entire tube could be clearly traced to
its termination, it formed an anastomotic loop at the periphery of
the dentine with an adjoining tube. The calcigerous tubes present a
diameter of the ^ t h of an inch, and they are separated by interspaces
equal to four of their own diameters. Each calcigerous tube gives off
many primary branches in its course, but is rarely seen to divide dicho
tomously until it begins to form its irregular sinuosities near the peri-
p ery of the tooth. In the transverse section figured, the primary
branches were sent off from the concave side of the tube, at an
acute angle with the trunk : the secondary smaller and more’ numerous
branches proceed from the same side of the main tube or of its
primary branches, at a less acute angle, into the clear uniting substance;
they are remarkably parallel with each other and straight,
n old poison-fangs the pulp-cavity tion of the remains of the pulp. or fissure is obliterated by ossificaThe
external layer of cement is very thin where it covers the crown
of the tooth; it is best seen at the line of union of the coadapted
margins of the inflected tooth c. At this part the cement is more
abundant m the viper’s tooth, and its transparency permits a bristle
inserted into the poison-canal to be seen through it. The layer which
coats the inflected surface of the fang is thinner than the outer one,
which, from its transparency, has been regarded as enamel. (1)
ffoorr the capsule m which the toIoth Ml fon Bned, a n1d tfhroamt t hthee P i°ninsoern -stuurbfaec Ie onfo wt hciocaht eitd i sw withel le nkanmoweln,
enamel gf deposed, does not pass between the edges of the slit into the poison tube ; as,
There is, however, no trace of true enamel upon the teeth of the
poisonous serpents any more than upon those of the innocuous species.
The cells of the cement are more minute and inconspicuous in the
poison-fang, than in the simple teeth of the Python and Boa.
The teeth of all Ophidians are developed and completed in the
original seat of the tooth-germs in all animals; viz. the mucous
membrane or gum covering the alveolar border of the dentigerous
bones. This gum presents the same lax tissue and is as abundantly
developed as in the Pike, Lophius, and many other fishes, in which it
likewise serves as the nidus and locality for the complete development
of the teeth.
The primitive dental papilla in the common harmless snake very
soon sinks into the substance of the gum and becomes inclosed by a
capsule. As soon as the deposition of the calcareous salts commences
in the apex of the papilla, the capsule covering that part becomes
ossified and adherent to the dentine, and the tooth begins to pierce
and emerge from the gum, before its mould, the pulp, is half completed.
Fresh layers of cells are successively added to the base of
the pulp, and converted by their confluence and calcification into the
tubular dentine, until the full size of the tooth is attained, when its
situation in the gum is gradually changed and its base becomes
anchylosed to the shallow cavity of the alveolar surface of the
bone.
In the posterior part of the large mucous sheath of the poison-fang,
the successors of this tooth are always to he found in different stages
of development; the pulp is at first a simple papilla, and when it has
sunk into the gum the succeeding portion presents a depression along
its inferior surface, as it lies horizontally, with the apex directed
backwards; the capsule adheres to this inflected surface of the
pulp. But how the cylindrical cavity of the dilated fold is occupied
in the loose growing poison-fang, and by what contrivance it is
however, it passes over that slit, it will cover it with enamel and in some cases by that means
alone the edges become soldered together.”—Philos. Trans. 1818, p. 473.
The author appears here to have been misled by the prevalent doctrines , of dental development
; no tissue of a tooth is deposited from a surface: a distinct convertible matrix or mould
is as essential to the formation of enamel, as of cement or dentine, and unless such organ be developed
from the inner surface of the capsule, no enamel can be formed.