POISON APPARATUS. 343 
jaw in the bone known as the anterior maxillary. All this class 
are venomous. They are known as the Proteroglypha, which 
means snakes with the anterior (front) maxillary teeth grooved 
or hollow. 
, RESULT OF INVESTIGATION. 
Our well-known Boomslang or Tree Snake (Dispholidus typus) 
is a member of the Opisthoglypha or Hind-fanged Snakes, which 
is generally believed to be at most very slightly venomous—only 
sufficiently so to enable it to paralyse its prey before deglutition. 
The reasons for this belief are based on the fact of the snakes 
of this class possessing imperfectly developed poison glands 
which are not connected with the grooved teeth by well-defined 
poison ducts, as is the case with the typical venomous snakes ; 
hence they are considered to be in a more or less rudimentary 
or transition stage. 
The results of my experiments with the Boomslang, given in 
detail in a former chapter, have, I think, conclusively shown 
that one member at least of this class of so-called slightly venom- 
ous snakes is as highly venomous as the Cape Cobra or Puff 
Adder. It is reasonable, therefore, to assume a good many of 
the others would, on investigation, be found to be equally 
venomous. Therefore, until each individual of this large division 
of snakes has been carefully experimented with, it would be unwise 
to lead the public to infer they were either practically harmless 
or only slightly venomous. In‘South Africa we have twenty-six 
species of these Hind-fanged Snakes so far recorded. 
PoIson APPARATUS. 
The venom of snakes is secreted by a pair of glands lying on 
each side of the skull beneath the skin, situated just under and 
behind the eyes. The Night Adder (Causus rhombeatus) is an 
exception to this rule. The venom glands are almond-shaped, 
and are composed of great numbers of cells. . Within the glands 
are cavities known as Alveoli. These are lined with short 
columnar cells. In these cavities the venom is stored until 
squeezed out by the contraction of the gland by certain muscles. 
The glands are termed Racemose Glands because the cells are 
