116 THE VITAL FUNCTIONS. 



like a valve in closing the air passage into the lungs. 

 If, when this animal has approached within a cer- 

 tain distance of the insect it is about to seize, we 

 watch it with attention, we are surprised to observe 

 the insect suddenly disappear, without our being 

 able to perceive what has become of it. This arises 

 from the frog having darted out its tongue upon its 

 victim with such extreme quickness, and withdrawn 

 it, with the insect adhering to it, so rapidly, that it 

 is scarcely possible for the eye to follow it in its 

 motion. The Cliameleon also has a very long and 

 lender tongue, the extremity of which is dilated 

 into a kind of club, or spoon, and covered with a 

 glutinous matter: M'ith this instrument the animal 

 catches insects at a considerable distance, bv a si- 

 milar manoeuvre to that practised by the frog.* 



As Serpents sw^allow their prey entire, so the 

 bones of their jaws and face are formed to admit of 

 great expansion, and freedom of motion upon one 

 another. Serpents and Lizards have generally 

 curved or conical teeth, calculated rather for tearing 

 and holding the food than for masticating it : like 

 those of tishes, they are affixed partly to the jaws, 

 and partly to the palate. The Chelonian reptiles 



* Mr. Houston has given a description of the structure of this 

 organ, and ot" the muscles by which it is moved, in a paper contained 

 in the Transactions of the Royal Irish Academy, vol. xv. p. 177. 

 He also describes a peculiar vascular structure by the rapid filling of 

 whicli with blood he conceives the elongation of the tongue may be 

 produced ; an effect, however, to which such a structure appears to 

 be wholly inadequate. Mr. Crampton has lately endeavoured to 

 explain the phenomenon of the quick propulsion of the tongue of 

 the Chameleon by the sudden blowing into its tubular cavity of a 

 small quantity of air furnished from a sac in the throat which com- 

 municates with the trachea. 



