THE BLOOD AND CIRCULATION 



263 



ries leave the heart prevent the backward flow of the 

 arterial blood. 



There are two main arterial trunks, (i) the pulmonary 

 which leads from the right ventricle and soon divides nto 

 the pulmonary arteries which supply the lungs; and (2) 

 the aorta which passes from the left ventricle and carries 

 the blood which supplies the greater part of the body. 

 Corresponding to the arteries which pass out from the 

 ventricles are two sets of veins emptying into the auricles, 



SVC 



FIG. 195. Diagram of inside of heart. AO, aorta; IVC, inferior vena 

 cava; LA, left auricle; LV, left ventricle; PA, pulmonary arteries; PV, 

 pulmonary veins; RA, right auricle; RV, right ventricle; SVC, superior 

 vena cava. 



(i) the pulmonary veins which bring blood from the lungs 

 to the left auricle, and the two vena cava which discharge 

 blood from the general circulation into the right auricle. 

 There are two systems of circulation connected with the 

 heart, the pulmonary which carries blood to and from the 

 lungs, and the systemic which carries blood to and from 

 the rest of the body. Nevertheless the same blood must 

 pass through both systems. 



In order to illustrate its course let us start with the 



