CIRCULATORY SYSTEM 



339 



auricle and ventricle and between the right auricle and 

 ventricle. Each of these openings is guarded by a 

 valve. These are so arranged that when they are closed 

 no blood can pass from the ventricles back into the 



auricles. 



Pulmonary 



Superior 

 Vena Cava 



Right - 

 Auricle 



Right 

 ,'entric 



Fig. 159. Diagram to show the internal structure of the heart. 



Connected with the heart are tubes called blood 

 vessels. The tubes which carry blood to the heart enter 

 the auricles and are known as veins. Those vessels 

 through which blood leaves the heart from the ventricles 

 are called arteries. 



