CHAPTER IX 

 THE HEART 



PROCURE a sheep's heart from a butcher with the " bag," 

 that is the pericardium, and the lungs, if possible, still attached. 

 If not, see at least that the point at which the vessels have been 

 cut is some distance from the heart. 



The Pericardium. The pericardium is a completely 

 closed bag in which the heart lies. It is formed of a thin 

 membrane which is transparent except near the large vessels, 

 where it is thickened by the presence of fat. When the bag 

 is cut open a little yellowish fluid, the pericardial fluid, may 

 escape. The heart hangs free in the bag, the pericardial mem- 

 brane being apparently attached only to the base of the heart, or 

 rather to the roots of the great vessels. The inner side of the 

 membrane is smooth and shiny, and the same is the case with 

 the surface of the heart. This is because the pericardium at 

 the base of the heart passes on in a thin layer over the whole 

 heart, firmly adhering to it, so that there are two parts of the 

 pericardium, one applied to the heart, and the other forming a 

 bag, and the one part is continuous with the other at the base 

 of the heart. 



The Heart. The heart is conical in shape and muscular 

 in nature, and contains four chambers. The base to which 

 the vessels are attached is uppermost ; the apex is lowermost. 

 You can tell the front because it is rounded and convex, and 

 has a groove filled with fat running from the upper part on 

 one side, obliquely downwards towards the other side. The 

 back is flatter than the front, and the groove containing fat 

 running down the middle of it is inconspicuous. Place the 

 heart before you with the front uppermost and the apex point- 



