POISON APPARATUS. 345 
salivary glands underwent a gradual change, and the fluid they 
secrete is now of a totally different character. In scientific 
terminology they are “‘ the homologues of the parotid salivary 
glands in other vertebrate creatures.” 
We find the venom glands and fangs of snakes in various 
stages of evolution. In the division known as the Aglypha, we 
do not find any trace of grooved fangs or poison glands, The 
teeth are all solid. In some of the species a few of the teeth are 
fang-like, being longer than the rest, but these also are quite 
solid. In the second division of snakes, which are known as 
the Opisthoglypha, the fangs are in various stages of develop- 
ment, and are situated half-way back in the upper jaw. There 
are usually two or three fangs, which are grooved. However, 
there are no well-defined poison glands with ducts, consequently 
this division of Hind-fanged Snakes has been regarded as practi- 
cally non-venomous. The Boomslang (Dispholidus typus) is a 
member of this division of snakes. 
In the third division, known as the Proteroglypha, we find 
the fangs and poison glands in a high degree of development. 
All of this class of snakes are known to be venomous to a greater 
or lesser degree. 
The fangs of the viper family are long and re-curved, and the 
bone they are set in is very mobile and works like a hinge. This 
provision of Nature is very necessary in order to elevate the 
fangs to allow of their points striking the victim at a proper 
angle. When the mouth closes, the fangs are automatically 
drawn back, and lie along the sides of the upper jaw, enveloped 
in a membranous sheath, known as the Vagina dentis. 
The fangs of Cobras are small in comparison with those 
of the Adders, and are incapable of much movement, such 
not being necessary for their effective use. They are received 
into a small cavity in the lower jaw when the mouth is 
closed. 
When the snake’s mouth is closed, the end of the poison 
duct becomes disconnected with the hole in the top or base of 
the fang, but the instant the mouth is opened to strike, the end 
of this duct, by means of an intricate and delicate apparatus, 
completes the connection with exactness. 
The instant the fangs penetrate the flesh of the victim, the 
snake closes his jaws over the bitten part and presses strongly, 
