304 



A COURSE ON ZOOLOGY. 



are very prominent and very mobile, and they can be 

 turned in opposite directions ; the long tongue can be 

 thrust far out to seize insects, and the round and pre- 

 hensile tail can grasp tree-branches, etc. The digits, like 

 those of parrots, are arranged in two opposing pairs on 

 each limb. The lungs are large, and when fully inflated 

 nearly double the bulk of the body. The common 

 chameleon rarely exceeds fifteen inches in length. 



FIG. 259. 



OPHIDIA. 



Serpents have no limbs ; their extremely elongated 

 bodies are moved by a series of lateral flexures. The 

 vertebrae and the ribs alone constitute almost the entire 

 skeleton. The water-adder has more than three hun- 

 dred vertebrae ; the viper about two hundred. The eyes 

 of serpents have a fixed appearance, caused by the 

 existence of but one eyelid ; this eyelid is fixed and 

 transparent, and covers the eyeball as would a watch- 

 crystal. The tongue is 

 long, slender, and ordi- 

 narily bifurcated ; it is 

 frequently thrust out, 

 and this has given rise 

 to the erroneous notion 

 that it could be used as 

 a sting. 



The mouth is always 

 armed with teeth, but 

 these organs are of lit- 

 tle service excepting to 

 retain the prey, which 

 is swallowed entire, after a process of softening and 

 crushing that sometimes lasts several days. The ex- 



POISON APPARATUS OF THE RATTLESNAKE. 



g, poison-gland, having a duct opening 

 into a canal in the fang ; m, muscles that 

 compress the gland and close the jaws ; 

 d, poison-fangs ; s, salivary glands ; /, 

 nostril. 



