DIVISIONS OF EEPTILIA. 



267 



of the iang, and is connected witli the duct of the "poison-gland." 

 This is a gland (tig. 19-2, a), .situated under and behind the eye, 

 secreting the poisonous fluid which renders the bites of these snakes 



Fig. 192.— The head of the RattlcsTiake, <lissfftp<l to show the p- 

 uitd poisi»u-l':uig.s {/). (After Duveriioy.) 



isoii-ghiiiil (a) 



dangerous or fatal. When the serpent strikes at muv animal, the 

 poison is forced through the poison-fang into the wound, partly by 

 the contractions of the nuiscular walls of the gland, and partly by 

 the compressive action of the muscles of the jaws and cheeks. 



The Ojyhidla are usually clas.sitied iu acconlance "witli the cliaraoters of their 

 deutal apparatus, ami may he divided as follows, some miuor groups heiug 

 omitted: (1.) The Viperina comprise the most typical of the venomous Sna]^e.s 

 [Veiienosa), and inelmle the coniuion Vipers [Viperida') and the Rattlesnakes 

 {Crotalidce), the former being confined to the Old World, whilst the latter are 

 mainly American. Tlie common Viper (Pelias herus) occurs abundantly in 

 Europe and Northern Asia, and is capable of inflicting a severe and even dan- 

 gerous bite. The rest of the true Vipers are African and Asiatic, well-known 

 examples being the Puff-adder o/ tlie (.'ape of Good Hope [Cloihi)), the Horned 

 Viper [Ctrastcs) of North Africa, and the '' Tic-polonga" (Daboia -Ru.'<s€Uii) of 

 India. 



The true Rattlesnakes [CmUdas) are exclusively natives of America, an 1 

 they are highly poisonous. The extremity of the tail in the common Rattle- 

 snake {Crotalus durissus) is furnished with a series of horny epidermic cells 

 of an undulated pyramidal shape, articulated one within the other, constituting 

 an appendage which is known as the '^ rattle. " Before striking its prey, the 

 Rattlesnake throws itself into a coil, and sliakes its rattle, as it does also when 

 alarmed. A nearly allied form (C horridus) is found in South A merica. Other 

 American examples of the Crotalldm nre the Fer-de-lance {Trif/i'uoccjihalus) 

 of the West Indies, the Copper-liead {Ancistrodon coni<ulrix]. and the Water- 

 mocassin {A. piscivorus), in which there is no rattle. In India ;>nd Southern 

 Asia there are also various Snakes belonging to the Cr(didi<J<r. 



Taken as a whole, tlie Viperiue Snakes are distinguished by having only a 

 single poison-fang on each maxilla ; while this bone is .sliort and niovalile, and 

 carries no other teeth, There are, however, one or more reserved'angs behind 



