ANATOMY OF THE I1EA11T AND BLOOD-VESSELS. 213 



The Position of the Heart. The heart (h, Fig. 1) lies 

 in the chest immediately above the diaphragm and opposite 

 the low^r two thirds of the breast-bone. It is conical in 

 form with its base or broader end turned upwards and pro- 

 jecting a little on the right of the sternum, while its narrow 

 end or apex, turned downwards, projects to the left of that 

 bone, where it may be felt beating between the cartilages of 

 the fifth and sixth ribs. The position of the organ in the 

 Body is therefore oblique with reference to its long axis. It 

 does not, however, lie on the left side as is so commonly sup- 

 posed but very nearly in the middle line, with the upper part 

 inclined to the right, and the lower (which may be more 

 easily felt beating hence the common belief) to the left. 



The Membranes of the Heart. The heart does not lie 

 bare in the chest but is surrounded by a. loose bag composed 

 of connective 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 itselX adhering closely to it. Each of the 

 3erous layers is covered by a stratum of flat cells, and in the 

 space between them is found a small .quantity of liquid 

 which moistens the contiguous surfaces, and diminishes the 

 friction which would otherwise occur during the movements 

 of the heart. *., / 



Internally the heart is also lined by a .fibroids membrane, 

 covered with a single layer of flattened cells* and called the 

 endocardium. Between the endocardium and- -the -visceral 

 layer of the pericardium the bulk of- the wall of the -heart 

 lies and is made up. mainly of striped muscular tissue (myocar- 

 dium) differing from that of '^he skeletal muscles; but con- 

 nective tissues, blood-vessels, nerve-cells, and nerve-fibres are 

 also abundant in it. 



Note. Sometimes the pericardium becomes inflamed, this 

 affection being known as pericarditis. It is extremely apt to 

 occur in acute rheumatism, and great care should be taken 

 never, even for a moment, except under medical advice, to 

 expose a patient to cold during that disease, since any chill 

 is then especially apt to set up pericarditis. In the earlier 

 stages ol pericardiac inflammation the rubbing surfaces on 



