THE HEART A DOUBLE PUMP 



IOI 



told the direction in which the current of blood flowed ; 

 it could flow only in one direction, from the auricle to 

 the ventricle. 



There was no need for Harvey to remind his audience 

 that there are no visible pores or passages between the 

 two ventricles ; that was admitted by all. It was also 



PULMONARY ARTERY 

 AORTA 



PULMONARY VEINS 



LOWER CAVAL 

 VEIN 



RIGHT VENTRICLE 



LEFT 

 VEN TRICLE 



Fig. 28. — A diagram to show the four chambers of the heart and the valves 

 which guard their openings. 



admitted that the right ventricle had only two openings. 

 One of them he had just described ; the other led into 

 the great channel for the lungs — the pulmonary artery 

 (fig. 28). He showed them that when the blood entered 

 this channel it could not flow back into the ventricle, as 

 they supposed it did, because the passageway was guarded 

 by a valve which closed automatically and prevented a 

 reflux. The valve at the pulmonary opening is made up 

 of three membranous pockets, similar in construction to 



