OHAPTEE VI. 



THE CIRCULATION OF THE BLOOD. 



THE blood is made to circulate within the system of closed tubes in 

 which it is contained by means of the alternate contraction and relaxa- 

 tion of the heart. The heart is a hollow muscular organ consisting of 

 four chambers, two auricles and two ventricles, arranged in pairs. On 



Pulmonary artery . 



Superior cava or vein 

 from head and neck 



Right auricle 

 Inferior vena cava 



Right ventricle ,. 



Portal circulation 



Second renal 

 circulation 



Pulmonary 

 capillaries 



Pulmonary veins 

 Aorta 



Arteries to head and 

 neck 



.. Left auricle 



Left ventricle 



Gastric and intestinal 



.First renal circulation 



___ Systemic capillaries 



Fig. 145. Diagram of the circulation. 



the right and left sides is an auricle joined to and communicating with 

 a ventricle, but the chambers on the right side do not directly commu- 

 nicate with those on the left side. The blood is conveyed away from 

 the left side of the heart (as in the diagram, fig. 145) by the arteries, 

 and returned to the right side of the heart 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. 

 From the right side of the heart the blood passes to the lungs 



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