2U 



VERTELllATA : IlEPTILIA OB EEPTILES. 



Pulmonary artery. 



Pulmonary vein 

 Hi "hi auricle.. 



Vuua cava 



Left arch of aorta. . 



aorta. 



Pulmonary artery. 

 Pulmonary vein. 



Left auricle. 

 Single ventricle. 



Ventral aorta. 



Keptilian Heart Turtle. 



auricles and only one ventricle. Crocodilians, however, 

 have two auricles and two ventricles. 



Therefore the impure or venous blood Avhich comes from the various 

 parts of the body into the right auricle, and the arterial or pure 

 blood which comes from the lungs into the left auricle, are both 

 poured into the one ventricle, and thus mixed together. At each con- 

 traction of this ventricle a part of this blood is sent to the lungs to be 

 purified, and the remainder goes into the circulation without having 

 been subjected to the influence of respiration. 



Thus the blood of Reptiles is never completely oxygen- 

 ated ; to a certain extent it is always impure, and hence 

 their temperature is correspondingly low, and their habits 

 are generally sluggish. In warm climates, however, some, 

 kinds as Lizards are very active. 



Reptiles breathe by means of lungs ; but, as might be 

 inferred from the facts already stated, their respiration is 

 not active ; they consume comparatively little oxygen, and 

 can remain alive a loner time beneath the surface of the 



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water. The cells of the lungs are larger and less numer- 

 ous than in the higher animals. Reptiles have no dia- 

 phragm, and there is no separation of the cavity of the 

 chest from that of the abdomen. 



