THE VENOM APPARATUS 435 



(2) Crotalince. 



These are very abundant. A large sensory pit leading down 

 to the maxilla will help in the diagnosis. 



The Lachesis is a jungle snake, and has its head covered by 

 small scales, never shields. It is also seen in Asia. 



The L. mutis is very deadly. It attains to 14 feet in length 

 and is very aggressive. It has enormous fangs. The tail is 

 short and covered by pointed scales, and not shields. 



The Fer de Lance is also very deadly. 



The Ancistrodon is a fatal reptile, but its venom has not been 

 much studied. The crown of the 'head is covered by large 

 shields which are in contact with each other. It is also present 

 in India and Southern Asia. 



The Crotalus or rattlesnake only exists in America. Its bite 



is exceedingly dangerous. Pigs are their sworn enemies and 



. eagerly devour them. Their resistance may be due to the thick 



layer of subcutaneous adipose tissue, which is but slightly 



vascular and slowly absorptive. 



THE VENOM APPARATUS. 



There are some non-poisonous snakes that possess poison glands, 

 but the means of inoculating the venom are absent. It is used in 

 digesting its prey. 



The venom gland of poisonous reptiles resembles the modified 

 parotid of adult persons. The venom gland is situated at the sides of 

 the head and behind the eyes. It is covered by the masseter muscle, 

 which when contracted presses upon the gland and forces out its 

 poisonous contents. In some snakes the gland is like a long ribbon 

 passing along one-third of the body underneath the skin. The gland 

 is always covered by a tough fibrous capsule attached to the articula- 

 tion of the lower jaw. When the animal bites, this capsule is pressed 

 upon and the venom is forced along the duct. The duct is situated 

 just above the line of the lip to a point below the eye, and ends in a 

 small papilla or "pocket" of loose mucous membrane into which the 

 base of the fang is inserted. There is one fang at each side in action 

 at the same time, but reserve ones are always ready, and should one 

 be broken it can readily be substituted. The venom runs along a 

 groove on the anterior surface of the tooth or fang, or down a canal 

 formed by the sides of the groove coalescing. The duct does not come 

 directly to this groove, but terminates in the papilla or small sac 

 described. Vipers have the longest fangs, nearly i inch in length. 

 The fang projects downwards and backwards in the closed mouth and 

 is firmly attached to the alveolar process. Owing to the free mobility 

 of the cranial bones the tooth can be made " erectile " for piercing. 



