CHAPTER X 



THE HEART AND THE BLOOD VESSELS 



The heart has been recognized as an important organ for a 

 longer time than any other part of the body, and numerous 

 phrases in literature show the fanciful, as well as mistaken, 

 ideas once held concerning its function. The expression "love 

 with all one's heart" is an example of the erroneous notion 

 that the heart has something to do with the emotions. In real- 

 ity the heart has but one function: it simply pumps the blood. 

 Location of the Heart. The heart is located in the thorax, 

 between the lungs, just a little to the left of the mid-line, and 

 back of the "breast bone." The rigidity of this bone prevents 

 one's feeling the heart under it, but the lower end of it pro- 

 duces a distinct "beat" which can be felt and seen between 

 the fifth and sixth ribs. It is swung freely in the thoracic 

 cavity, attached to its upper wall by masses of connective 



tissue, which also bind it 

 to the large arteries and 

 veins, and to the wind- 

 pipe. 

 Pleura 



Trachea 



The Coverings and 

 Structure of the Heart. 



The heart is completely 

 enveloped by a two- 

 layered bag, the pericar- 

 dium (Fig. 73), which is 

 pierced only by the large 

 arteries and veins leaving 

 and entering the organ. 

 The inner layer of the pericardium is grown fast to the heart 

 muscle^ and thus forms a firm, tough covering for it; th 



FIG. 73. DIAGRAM 



Showing the relations of heart, lungs and 

 membranes around them. 



