02 



THE HUMAN BODY. 



5, The apex, or point, of the heart is just beneath the 

 fifth rib. Its base is a little to the right of the breast- 

 bone. It extends up as high as the third rib. It is held 

 in place by the diaphragm beneath it, and the large blood- 

 vessels which run into and out of it. It is about as large 

 as the fist, weighing from eight to twelve ounces. 



6, We find, on examining the interior, that it is divided 

 into four cavities. There is a division which runs across, 



Pulmonary artery. 



Aorta. 



Vena cava superior. 



Pulmonary veins. *"...... 



Right auricle. - 



Tiicuapid valve /; 



Vena cava inferior - 



Right ventricle. ' 



Pulmonary artery. 



-.Pulmonary veins. 



Left auricle. 

 Mitral valve. 



Left ventricle. 



Aorta. 



Fig. 29. 

 REPRESENTATION OF A SECTION or THE HEART (Diagrammatic). 



and one which runs lengthwise. This last divides it into 

 right and left sides, the other into auricles (Latin, auricula, 

 the external ear) and ventricles (Latin, ventricnlus, the 

 belly). These cavities are of nearly the same size, each 

 holding about three ounces. The walls of the auricles 

 are thin and loose. The wall of the right ventricle is 

 about a sixth of an inch thick. That of the left ventricle 

 is half an inch thick. 



7, The two large veins which bring the blood from the 



