148 VENOMS 
enormous dimensions. They may attain the size of a large 
almond (Crotalus, Naja), and they then occupy the spacious 
chamber already described (Chap. I., p. 10), which is situated 
behind the eye on each side of the skull. 
Each gland is surrounded by a thick capsule of fibrous tissue, 
two prolongations of which, the one anterior, the other posterior, 
keep it in its place beneath the masseter muscle. A portion of 
the latter is inserted in the capsule itself, in such a way that 
when the snake closes its jaws to bite, the gland is forcibly com- 
pressed and the contained liquid is squeezed into its excretory duct. 
“Between the muscle and the envelope of the gland there is 
a serous pouch, which enables the one to slide over the other. 
The excretory duct runs along the outer side of the upper jaw, 
and opens by a slit at the base of the poison-fang, with which 
it inosculates at right angles in a little muscular mass forming a 
sphincter. 
In the normal position of repose, the poison-fang is always 
concealed by a gingival fold of mucous membrane, in the sub- 
stance of which are buried a few fibres of the tendon of the 
internal pterygoid muscle. When the latter contracts, the tooth 
is almost completely exposed, and the efferent duct of the gland 
then assumes an oblique position, which allows of the direct dis- 
charge of the venom through the canal which runs along the 
sreater portion of the length of the tooth. 
When the poison-fangs are folded back in their sheath, the 
poisonous secretion can escape freely into the buccal cavity by 
the slit situated at the base of the fangs. 
At the moment when the animal is about to bite, when it 
throws back its head and opens its jaws, directing its fangs for- 
wards, the muscles that come into action (masseters, temporals, 
and pterygoids) compress the glands on each side, and cause the 
venom to be expelled in a sudden jet, as if by a sort of ejaculatory 
process. In the case of certain species the venom may be projected 
to a distance of more than a yard. 
