196 THE HUMAN &ODT. 



chest, but is surrounded by a loose bag composed of con- 

 nective tissue and called the pericardium. This bag, like 

 the heart, is conical but turned the other way, its broad 

 part being lowest and attached to the upper surface of the 

 diaphragm. Internally it is lined by a smooth serous mem- 

 brane like that lining the abdominal cavity, and a similar 

 layer (the visceral layer of the pericardium) covers the out- 

 side of the heart itself, adhering closely to it. In the space 

 between the serous membranes is a small quantity of liquid 

 which moistens the contiguous surfaces, and diminishes the 

 friction which would otherwise occur during the movements 

 of the heart. 



Suppose a pear put in a bag of about the same shape, 

 but larger, and turned the other way so that the big end 

 of the bag was round the small end of the pear; then you 

 will get a good idea of how the pericardium lies with refer- 

 ence to the heart. If the outside of the pear and the inside 

 of the bag were covered with paint, this would represent 

 the serous membrane, and a few drops of water between the 

 pear and the bag would represent the serous liquid. To 

 complete the comparison we may imagine the pear to 

 have eight or nine stalks which reached out from it through 

 the bag; these would answer to the blood-vessels entering 

 and leaving the heart. 



Note. Sometimes the pericardium becomes inflamed, 

 this affection being known as pericarditis. It is extremely 

 apt to occur in rheumatic fever, and extreme care should 

 be taken never, even for a moment, except under medical 



What is the pericardium? What is its form? What lines it? 

 What covers the outside of the heart? What lies between the visceral 

 layer of the pericardium and the outer bag? W nat is i ts use ? 



Illustrate the relations of heart and pericardium. 



What is pericarditis? In what disease is it especially apt to occur? 



