OF THE POISON-FANGS IN SEIIPENTS., 419 
and the vertical or ascending lamina is in consequence 
completely formed. The convex surface, moreover, of the 
poison-canal is at all times stronger and more compact than 
the lateral or concave portions. In one of the preparations 
now before me, there is an appearance indicating that the 
vertical lamina becomes first ossified on the side of the 
poison-canal. 
The opening at the base, by which the poison is at a fu- 
ture period to pass into the poison canal, is formed in a si- 
milar way with the anterior aperture or -outlet, yet there 
are certain differences arising out of the functions which 
the tooth must afterwards perform. The principal of these 
is the imperfect state of the aperture at its base, which can 
scarcely be called complete, and, indeed, is in some mea- 
^ sure rendered so only by its insertion into the maxillary 
bone. Anterior to, and on the sides of, the aperture, at the 
base of the fang, the external parietes of the tooth becomes 
very strong ; they are firmly united to the edges of the poi- 
son canal, and consequently, the greater portion of the 
nourishing pulp of the tooth is thrown towards the concave 
side ; but there still exists a very thin layer of pulp on the 
sides and lateral convex aspect, excepting always in the sit€ 
of the vertical lamitia, or uniting plate of the two canals. As 
the fixed fang is detached by a process which 1 shall imme- 
diately endeavour to describe, the rudimentary one, which 
has now attained its full growth (though not its hardness), 
becomes gradually fixed into the cavity on the lower sur- 
face of the upper maxillary bone, externally or internally, 
and by adhering to the edge of this bone, and, at the same 
time, advancing forwards, the source of nourishment of the 
pulp belonging to the poison canal is cut off, the portion of 
pulp at the time in the canal dies and wastes away ; and thus, 
for the first time, the osseous tube destined to give passage 
to the poisonous secretion becomes pervious. 
p d S 
