472 Mr. Smith on the structure of 
was produced by a perforation passing through the pulp ; 
this is not, however, the case, the tube being completely 
external, and formed by a deep longitudinal depression on 
the surface of the pulp. 
In order to render this more clear, I must here observe 
that a slight longitudinal furrow, or depression, is to be seen 
on all the teeth of the cobra de capello ; on those which are 
nearest to the poisonous fangs it is most evident, and occupies 
the convex side of their curvature ; it however is confined 
entirely to the parietes of the tooth, and does not at all affect 
the form of its cavity. 
But in the poisonous fangs, this depression is sunk deep into 
the substance of the tooth, and occupies a portion of the 
space, which in the others is allotted to the cavity which con- 
tains that part of the pulp which remains when the tooth is 
completely formed ; and the edges of the depression being 
brought together along the greater part of the tooth, form 
the slit or suture that I have before described, but, being 
kept at a distance at both extremities, there results a foramen 
at the base and at the apex. 
That this is a correct view of the mode in which the poi- 
sonous tube is formed, receives additional support from what 
I have observed in a 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 supports the poisonous fangs. These teeth so 
much resemble the fangs, that it requires a very close inves- 
tigation 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 
