its cervical integument can be expanded into a hood, constitutes an
immediate link between the Bungarus and Naja.( 1)
The superior maxillary bone diminishes in length with the
decreasing number of teeth which it supports: the transverse or
external pterygoid bone elongates in the same ratio, so as to retain its
position as an abutment against the shortened maxillary, and the
muscles implanted into this external pterygoid style communicate,
through it, to the maxillary bone the hinge-like movements backwards
and forwards upon the ginglymoid articulations connecting that
bone with the anterior frontal and palatine hones. As the fully
developed poison-fangs are attached by the same firm basal
anchylosis to shallow maxillary sockets, which forms the characteristic
mode of attachment of the simple or solid teeth, they necessarily
follow all the movements of the superior maxillary bone; when the
external pterygoid is retracted the superior maxillary rotates backwards,
and the poison-fang is concealed in the lax mucous gum, with
its point turned backwards i when the muscles draw forward the
external pterygoid, the superior maxillary bone is pushed forwards
and the recumbent fang withdrawn from its concealment and
erected.
In this power of changing the direction of a large tooth, so that it
may not impede the passage of food through the mouth, we may perceive
an analogy between the viper and the lophius; but in the fish the movement
is confined to the tooth alone, and is dependent on the mere
physical property of the elastic medium of attachment: in the
Serpent the tooth has no independent motion, but rotates with
the jaw, whose movements are governed by muscular actions. In the
fish the great teeth are erect, except when pressed down by some
extraneous force : in the Serpent the habitual position of the fang is the
recumbent one, and its erection takes place only when the envenomed
blow is to be struck.
The peculiar structure of the poison-fang was first described
by Fontana as it exists in the viper (2), and subsequently received addi-
(1) Dr. Canter, Proceedings of the Zoological Society, 1838, p. 73.
(2) Fontana’s description is as follows : “ The tooth of the viper has a double pipe or tubule
almost for its whole length, a circumstance hitherto entirely unknown to observers. These two
tional elucidation by Mr. Smith’s careful examinations of the fangs
of the Hydrus, Naja and Crotalus, and by Mr. Clift’s illustrative
drawings appended to Mr. Smith’s Paper(l). A true idea of the structure
of a poison-fang will be formed by supposing the crown of a simple
tooth, as that of a Boa, to be pressed flat, and its edges to be then bent
towards each other, and soldered together so as to form a hollow cylinder
open at both ends. The flattening of the fang and its inflection
around the poison-duct commences immediately above the base, and
the suture of the inflected margins runs along the anterior and convex
side of the recurved fang : the poison-canal is thus in front of the pulp-
cavity. The basal aperture of the poison-canal is oblique and its opposite
outlet is still more so, presenting the form of a narrow elliptical longitudinal
fissure terminating at a short distance from the apex of the
fang. The relative position of the two apertures of the poison-canal
is shown in the figure of the fang of the large Cobra (PI. 65, fig. 9),
where a fine hair is represented as passing through the poison-canal :
in figure 1 1 , the relative position of the pulp cavity, a, to the poison-
canal, b, b, is shown in the plan of a longitudinal section of a poison-
fang.
The character most commonly adduced from the dental system
as distinguishing the venomous from the non-venomous serpents is
that the former have two, the latter four rows of teeth in the upper
jaw : the two outer or maxillary rows being wanting in the venomous
species and their place being supplied by the single poison-fang. (2)
canals or tubes do not communicate with each other, and are separated by a bony partition,
very brittle towards the basis, but which becomes somewhat stronger in proportion as it advances
towards the point. One of these tubes or canals, which I call the external one, because it is at
the side of the convex part of the tooth, begins, as has been seen, at the basis of the triangular
opening, and goes on enlarging by degrees to the middle of the length of the tooth, whence it
gradually narrows, and ends at the elliptical opening of the point. The inner canal on the contrary,
which is towards the concave part of the tooth, begins with a large opening at the basis,
from whence it advances, closing by degrees, and terminates at length in a blind point above the
middle of the tooth. The partition likewise that separates the two cavities is crooked, and its
convex part is turned towards the hollow of the canal it terminates. The blind canal communicates
yith the socket in which the tooth is fixed, and receives vessels and nerves.”—Fontana,
On Poisons, Part I. Treatise on the Venom of the Viper, &c., translated by Skinner, 8vo.
2d Ed. 1795, p. 10. (The original Treatise was published in Italian, in 1765.)
(1) Philos. Trans. 1818.
(2) Compare figure 13, Naja, with fig. 6, Python, in Plate 65: the letter b shows the
Q 2