18 



KEPTII.K GALLEKY. 



longer than the rest, but they are not grooved or perforated, nor 

 do they communicate with a poison-gland. 



The poisonous Snakes are armed with a long canaliculated tooth 

 in front of the upper jaw ; the channel terminates in a small slit 

 at the extremity, and is in connection with a duct which carries 



Fig. 14. 



■? 



m 



Skull of Poisonous Snake (Vipera nasieornis). 



m, maxillary, with poison-fang- ; a bristle is inserted in the openings of the 

 channel at the base and point of the tooth ; d, undeveloped poison- 

 fangs; 2 }m , premaxillary ; q, quadrate bone. 



the poisonous fluid from a large gland to the tooth. This venom- 

 gland is situated on the side of the head, above the angle of the 

 mouth, and invested by a dense fibrous sheath, which is covered 

 by a layer of muscular fibres. At the moment the Snake opens 

 its mouth to bite, the muscles compress the gland, and force its 

 contents through the excretory duct into the channel of the venom- 

 tooth, whence it is ejected into the wound. The force with which 

 the gland is compressed is shown by the fact that irritated animals 

 have been seen to spout the poison from the aperture of the tooth 

 to a considerable distance. The venom-apparatus serves these 

 creatures not only for defence, but also, and chiefly, for the pur- 

 pose of overpowering their prey, which is always killed before they 

 commence to swallow it. 



The dental apparatus is not the same in all poisonous Snakes. 

 The venom-tooth is always fixed to the maxillary bone ; but in 

 some this bone is as long, or nearly as long, as in the non-venomous 

 Snakes, and generally bears one or more ordinary teeth on its 

 hinder portion. This venom-tooth is always more or less erect, 



