TR 



BR 



P V 



L A 



I VC 



PV 



LV 

 B V 



THE HUMAN HEART 



There are four chambers, two auricles or receiving chambers and two ventricles or driving 

 chambers. The right auricle (RA) receives the impure blood from the body by two superior 

 venae cavae (SVC) and one inferior vena cava (IVC). 



The blood ib passed into the right ventricle (RV), whence it is driven to the lungs through 

 the pulmonary arteries (PA). From the lungs the purified blood returns by the pulmonary 

 veins (PV) to the left auricle (LA). 



From the left auricle it passes to the left ventricle (LV) t whence it is driven up the systemic 

 arch (SA) to the body. The systemic arch first gives off a right innominate artery (INN, 

 dividing into right subclavian and right carotid, to arm and head respectively). It then gives 

 off a left carotid (C) and a left subclavian (SCL), to head and arm respectively. It is con- 

 tinued dorsally backwards to form the dorsal aorta (DA), the great artery distributing pure 

 blood to the whole posterior body. 



TRis the windpipe or trachea; BR, a bronchial tube carry ing air to the lungs; BV, a blood- 

 vessel on the wall of the heart itself. 



A B. C. 



Reproduced by permission from Keith's " The Engines of the Human Body" (Wil- 

 liams C7* Norgate). 



A, a swelling on a vein, indicating the presence of a valve within it. B, the 

 vein laid open, showing the valves partly open: blood flowing in the direction of 

 the arrow will have free passage between the valves. C, showing the valves 

 shut; blood forced backwards in the direction of the arrows will find the valves 

 closed against it. 



