416^ ON THE GROWTH AND STRUCTURE 
taken notice of the head of a common viper, in which I 
found two poison-fangs fixed into either maxillary bone ; 
but such an occurrence must be exceedingly rare, for of 
the vast number of poisonous snakes I have examined in 
this and in other countries, the viper alluded to is the only 
instance in which I have met with it. 
Whatever be the situation of the fixed fang, there will 
always be found a rudimentary one, partly attached to the 
bone, and preparing to occupy the vacant space described 
above, and to replace the old tooth, whenever by age or 
other causes the latter may have been detached from its 
socket, and separated from the animal. But previous to 
describing the mode in which we may suppose this process 
of decay and renovation to be effected, it is essential to ex- 
plain to the Society the real structure of the fangs them- 
selves. 
It is, I think, sufficiently well known, that, in addition 
to the fixed poisonous teeth, serpents possessing these dan- 
gerous organs have others which may be called rudiment- 
ary ; that is, they have on either side, close to the fixed 
fang, and suspended to the upper jaw, a certain number of 
teeth, intended by nature to supply the deficiency in the 
fixed teeth, whenever these shall have been shed or lost. 
The rudimentary teeth I speak of, are entirely surrounded 
by soft parts, each inclosed in a separate sheath, and cannot 
be seen without dissection. They seem to me to be in a 
constant state of growth, and indeed present a regular se- 
ries, from a mere horny point to a tooth, nearly equalling 
in size, strength, and hardness, the one actually employed, 
and at the time fixed. We may either consider the tooth 
as it first appears, tracing it through its various stages to 
the full-grown tooth, or vice versa. The first mode seems 
the most natural, and it is the one I shall adopt. 
At whatever time a poisonous serpent is examined, there 
