540 



GENERAL CHARACTERS OF REPTILES. 



the Proteus, Siren, and Axolotl (Fig. 345) are of this number; 

 but most Reptiles have only lungs. It does not follow from 



FIG. 315 ANATOBIY OF COLUBER. 



I, tongue and glottis ; ce, aesophagus, divided at <K' to show the heart, &c. ; f , stomach ; 

 i', intestine ; cl, cloaca; on, anus ; /, liver ; o, ovary ; 6, eggs ; /, trachea ; p, principal 

 lung ; p', undeveloped lung ; vt, ventricle ; c, left auricle ; c', right auricle ; ag, left 

 aortic arch ; ad, right aortic arch ; d. d, ventral aorta ; ac, carotid arteries ; v, vena 

 cava superior ; vc, vena cava inferior ; vp, pulmonary vein. 



this, however, that their respiration is always exclusively aerial ; 

 for in several of these animals, the skin is also an organ of respi- 

 ration, and can act upon the air contained in the water, as well 



