148 VENOMS 



enormous dimensions. They may attain the size of a large 

 ahiiond {Crotalus, Naja), and they then occupy the spacious 

 chamber ah'eady 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 viasseter 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 

 greater 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. 



