350 SNAKES. 



First, the ' fangs ' of the harmless snakes, such as Lycodon, 

 Xeiiodoii, Heterodoii, etc., which have no poison gland, but 

 whose saliva may be slightly and occasionally injurious. 



Secoiidly, those having a salivary gland secreting poison 

 and a grooved fang in front of some simple teeth, Hydro- 

 pJiidcB, 



Thirdly, the maxillary bone shorter, bearing one poison 

 fang with a perfect canal, and one or two teeth behind it. 

 In some of these there is a slight mobility. 



Fourthly, the maxillary bone so reduced as to be higher 

 than long, and bearing only a single tooth, viz. a long, 

 curved, and very mobile fang, Viperina. 



These four classes, be it observed, are only designated 

 ' roughly speaking.' Nicholson describes a close gradation 

 in the development of the poison glands also to correspond 

 with those almost imperceptible stages. The poison gland is 

 after all only a modified salivary gland. It lies behind the eye, 

 whence the venom is conveyed by a duct to the base of the 

 fang, down along it, and sometimes through it, and is emitted 

 at what we may for the present call the point, into the wound 

 made by it, something on the principle of an insect's sting. 

 As when inserting the sting the pressure forces the poison 

 out of a gland at its base, so does the pressure of certain 

 muscles act upon the poison gland when a snake opens 

 its mouth to strike. In some of the most venomous, viz. 

 the viperine families, the largely developed glands give that 

 peculiar breadth to the head. There is a hideous, repulsive 

 look about some of these, that seems to announce their 

 deadly character, even to those who see one for the first 

 time. The evil expression of the eye, with its linear pupil ; 



