258 



PHYSIOLOGY. 



venous blood which is returned from all parts of the body, 

 and sends it through the* lungs, from whence it returns to 

 the left side of the heart changed to bright arterial blood, 

 and is distributed by the aorta, or great artery, through the 

 system. The right heart then may be called the venous or 

 pulmonary heart, the left, the arterial heart. Both, however, 

 are so united together, as to form in appearance but one 

 heart. 



Fig. 1. 



View of the heart inclosed in its bag, or pericardium, which is a se- 

 rous membrane. It is here laid open and turned back. 



8. Each of these hearts has two separate cavities ; one to 

 receive the blood, and the other to pump it out. The cavi- 

 ties which serve as receptacles, are called auricles, those 





