the poisonous fangs of serpents. 473 
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 longitudinal depression are rounded, we 
shall have a cylindrical cavity (the poison tube) nearly 
surrounded by a semilunar one (the cavity which contains 
the pulp). This is shown in the annexed drawings of the 
fangs of the cobra de capello. (PI. XXII. E. F. G. H.) 
If, however, the edges of the depression should be angular 
(as in the rattle snake), the horizontal section shows a figure 
somewhat different, the poison tube being more completely 
surrounded by the cavity which contains the pulp. This is 
shown in the drawing by the section 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. XXII. I. K.) 
In sections taken at different parts of the fang, the propor- 
tions 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 
