IOO 



THE CIRCULATION. 



technically called the circulation. The purposes for which 

 this unceasing current is maintained, are indicated in the 

 uses of the blood enumerated in the preceding chapter. 



The blood is conveyed away from the heart by the 

 arteries, and returned to it by the veins ; the arteries and 

 veins being continuous with each other, at one end by 

 means of the heart, and at the other by a fine network of 

 vessels called the capillaries. The blood, therefore, in its 

 passage from the heart passes first into the arteries, then 

 into the capillaries, and lastly into the veins, by which it 

 is conveyed back again to the heart, thus completing a 

 revolution, or circulation. 



Fig. 31.* 



Right 

 Lung. 



Pulmonary 

 _ Artery. 



As generally described there are two circulations by 

 which all the blood must pass ; the one, a shorter circuit 



* Fig'. 31. View of heart and lungs in situ. The front portion of 

 the chest-wall, and the outer vv parietal layers of the pleurae and peri- 

 cardium have been removed. The lungs are partly collapsed. 



