458 - On the Structure of 
That this is a correct view of the mode in which the poisonous 
tube is formed, receives additional support from what I have 
observed ina species of the genus hydrus of Schneider. In this 
serpent, as in many others nearly allied to it (les hydres of 
M. Cuvier), there are simple teeth on the same bone which sup- 
ports the poisonous fangs. These teeth so much resemble the 
fangs, that it requires a very close investigation to distinguish 
between them; and this arises from the simple tooth having not 
only a longitudinal furrow exactly resembling the edges of the slit 
of the poisonous fang, but also a very visible cavity at the base, 
where the foramen occurs in the others; and I have even found 
a fine tube in a tooth of this sort; it was however confined to 
the parietes, and did not affect the cavity of the tooth. 
To this gradation from a slight superficial furrow to a deep 
depression, may be added the fact, that no traces of either are 
observable in the teeth of those serpents which are not armed 
with venomous fangs: this I found to be the case in a large 
species of boa. 
As a consequence of the structure that I have described, if a 
horizontal section be made of a poisonous fang, in which the 
edges of the longitudinak depression are rounded, we shall have a 
cylindrical cavity (the poison tube) nearly surrounded by a semi- 
lunar one (the cavity which contains tae pulp). This is shown 
in the annexed drawings of the fangs of the cobra de capello.— 
(PLV EP Gye.) 
If, however, the edges of the depression should be angular (as ~ 
in the rattle-snake), the horizontal section shows a figure some- 
what different, the poison tube being more completely surrounded 
by the cavity which contains the pulp. This is shown in the 
drawing by the seetion of a fang of an unknown species of serpent, 
which has exactly the same form as that of the rattle-snake, but 
is twice as large. (PI. V. I. K.) 
In sections taken at different parts of the fang, the proportions 
between the poison tube and the cavity which contains the pulp 
will be different; the latter greatly increasing towards the base 
of the tooth; and near the apex the poison tube only will be 
seen, the fang at that part being solid. In a section also of a 
completely formed fang, the poison tube, at its anterior part, 
will be closely invested by the thickened parietes of the cavity 
which contains the pulp; this cavity however is never obliterated, 
but exists in all the teeth of serpents, even when they have ar- 
rived at their full growth. 
In the fangs, when completely formed, the edges of the slit, 
or suture, are frequently soldered together; when they are an- 
gular, so large a surface comes in contact, that they appear to be 
united by bony matter; in the cobra de capello, where they are 
rounded, 
