CHAPTER XVIII 

 THE HEART 



The general function of the heart should be clear in the 

 light of what has gone before. It is the double force 

 pump at the center of the circulation. It is conveniently 

 thought of as being about the size of the individual's 

 fist and it is placed in the chest between the lungs. 



FIG. 59. Suggesting the position of the heart in the thorax. 



More than half of it is to the left of the mid-plane. It is 

 an irregular cone with its apex directed downward, for- 

 ward, and to the left. This apex comes close to the wall 

 of the chest between the fifth and the sixth ribs, a fact 

 easily remembered in connection with II Samuel III, 27. 

 The heart is enclosed by a sac called the pericardium 

 which is really a continuation of its outer layer, reflected 



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