This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
The heart (h, Fig. 4) lies in the chest, immediately above the diaphragm and opposite the lower two thirds of the breast-bone. It is conical in form, with its base or broader end turned upwards and projecting 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. It does not, however, lie on the left side, as is so commonly believed, 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 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 membrane like that lining the abdominal cavity, and a similar layer (the visceral layer of the pericardium) covers the outside 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.
What then happens to it? How are the small arteries formed? In what vessels do they end? What becomes of blood which has flowed through the capillaries? Where do the veins carry it? How is back-flow prevented? How frequently does the heart receive and pump out blood?
Where is the heart situated? What is its form? Where does its base lie? Where its apex? Where may we feel the apex beat? What is the origin of the common belief that the heart is on the left side?
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 reference 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 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 of pericardiac inflammation the rubbing surfaces on the outside of the heart and the inside of the pericardium become roughened, and their friction produces a sound which can be heard with a stethoscope. In later stages great quantities of liquid may accumulate in the pericardium so as to seriously impede the heart's beat.
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? What is its use?
Illustrate the relations of heart and pericardium.
What is pericarditis? In what disease is it especially apt to occur?