202 NATURAL HISTORY. 



with a transparent membrane which is shed with the 

 skin. The tongue is soft, and forked at its end, and it is 

 not very sensitive. The smell and the touch are both 

 rather dull. Serpents have teeth, but not for mastication. 

 They only serve to retain their food. 



335. The species of this order may be grouped in two 

 classes — the Viperine and the Colubrine Snakes. The 

 Viperine Serpents have a peculiar venomous apparatus. 

 There are two teeth or fangs in the upper jaw, connect- 

 ed with the gland in which the poison is made. They 

 are movable, and when the animal does not wish to use 

 them, they lie backward, concealed along the roof of the 

 mouth. When the serpent bites, he throws these fangs 

 forward, and, at the same time, a muscle, pressing on the 

 gland, forces out the venom, which passes along a canal 

 in the fang. Most of the Colubrine Snakes are not ven- 

 omous, and those which are have stationary instead of 

 movable fangs. 



336. There are two families of the Viperine Snakes — 

 the Viperidae and the Crotalidse. The Viperidae belong 

 exclusively to the eastern hemisphere. Those of the trop- 

 ical regions are the most venomous. To this family be- 

 longs the Horned Viper, so called from a small pointed 

 horn above each eye. This is supposed to be the Asp, 

 from whose bite Cleopatra died. The Puff Adders of 

 Africa also belong to this family. 



337. Of the family Crotalidae, the true Rattlesnakes, 

 Fig. 164 (p. 203), are confined to this country, but there 

 are other species found in Asia. The rattle consists of 

 a number of thin, horny appendages, which are loosely 

 jointed together, and which make a rustling noise when 

 the snake moves. The number of joints is increased, up 

 to a certain amount at least, with each casting of the skin. 



338. The Colubrine Snakes have two famiUes — the Co- 

 lubridae or Colubers, and the Boidae or Boas. The fami- 

 ly of Colubers contains more than half the whole number 

 of species of Snakes. Of the comparatively few of these 



