254 



THE SCIENCE OF LIFE. 



scales, or horny plates, or spines. In the Iguanidce it is 

 elevated into a crest, or mane, of horny scales, covering 

 also the throat-pouches. The Draco volans, or Flying 

 Lizard, has a cutaneous expansion from the false ribs 

 which enable it to take short flights through the air. 



FIG. 151. A. Head of Harmless Snake. 1). Heads of Poisonous Snakes of different 

 genera. 



The tongue is bifid in many of this order, but in Cha- 

 meleons it is a long, round, muscular organ, clubbed at 

 the end, and coated with a viscid secretion, by means of 

 which it catches great numbers of flies by shooting it 

 out with remarkable speed. 



3. Chelonia, or Tortoises and Turtles. These resemble 

 Amphibians in some respects, but their structure is very 

 peculiar. The exoskeleton unites with the endoskeleton, 

 forming the carapace, or case, which includes the viscera 

 and muscular system. The vertebrae are soldered to- 

 gether and the ribs are expanded, making the walls of 

 the carapace. The ventral piece is called the plastrom, 

 or sternum. (Fig. 152.) 



