THE ANATOMY OF THE HEART AND BLOOD-VESSELS 325 



Between the endocardium and the visceral layer of the pericar- 

 dium the bulk of the wall of the heart lies and is made up mainly 

 of the special cardiac muscular tissue previously described (p. 86) ; 

 but connective tissues, blood-vessels, nerve-cells, and nerve-.fibers 

 are also abundant in it. 



Note. Sometimes the pericardium becomes inflamed, this af- 

 fection 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 of pericardiac inflam- 

 mation 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 recognized through the stethoscope. 

 In later stages great quantities of liquid may accumulate in the 

 pericardium so as seriously to impede the heart's beat. 



The Cavities of the Heart. On opening the heart (see diagram, 

 Fig. 101) it is found to be subdivided by a longitudinal partition 

 or septum into completely separated right and left halves, the 

 partition running from about 

 the middle of the base to a point 

 a little on the right of the apex. 

 Each of the chambers on the 

 sides of the septum is again in- 

 completely divided transversely, 

 into a thinner basal portion into 

 which veins open, known as 

 the auricle, and a thicker ap- 

 ical portion from which arteries 

 arise, called the ventricle. The 

 heart thus consists of a right 

 auricle and ventricle and a left 

 auricle and ventricle, each auricle communicating by an auric- 

 uloventricular orifice with the ventricle on its own side, and there 

 is no direct communication whatever through the septum between 

 the opposite sides of the heart. To get from one side to the other 

 the blood must leave the heart and pass through a set of capillaries, 

 as may readily be seen by tracing the course of the vessels in 

 Fig. 99. 



P d 



FIG. 101. Diagram representing a sec- 

 tion through the heart from base to apex. 



