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CHAPTER XIX 



THE HEART 



282. The heart. The blood is kept flowing through all 

 parts of the body by the heart. The heart is essentially a 



hollow shell of muscles, which 

 has the power of squeezing its 

 sides tightly together, so as to 

 force out the blood. It is coni- 

 cal in shape. Its side lies upon 

 the diaphragm, with its tip 

 c b pointing downward, forward, 

 ^ and to the left. Its small end 

 touches the chest wall about 

 two and a half inches to the 

 left of the lower end of the 

 sternum or breastbone, and its 

 large end extends along the 

 right side of the breastbone, 

 from its lower end upward as 

 high as the third rib. It is 

 almost covered by the lung, 

 and is inclosed in a bag of 

 serous membrane called the 

 pericardium. The pericar- 

 dium is very smooth, so as to permit free movements of 

 the heart within it. (See cut, p. 66.) 



162 



The heart. 

 a, right ventricle. 

 b left ventricle. 

 c artery between the two ventricles, 



nourishing the heart's muscles. 

 d pulmonary artery. 



left auricle. 



aorta. 



artery to left side of head. 



artery to left arm. 



artery to right side of head. 



artery to right arm. 



descending vena cava. 



right auricle. 

 m ascending vena cava. 



