POISON APPARATUS. 345 



we term Evolution, these harmless 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 typiis) 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 recurved, 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 enveloped 

 in a membraneous covering when at rest. 



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 its jaws over the bitten part and presses strongly. 



