204 



THE HUMAN BODY. 



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

 endocardium. Between the endocardium and the visceral 

 lay er of the pericardium the bulk of the wall of the heart lies 

 and is made up mainly of striped muscular tissue (differing 

 somewhat from that of the skeletal muscles) ; but connective 

 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 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 recognized through the stethoscope. 

 In later stages great quantities of liquid may accumulate in 

 the pericardium so as to seriously impede the heart's 

 beat. 



The Cavities of the Heart. 



cs 



On opening the heart (see 

 diagram. Fig. 78) it is 

 found to be subdivided 

 by a longitudinal parti- 

 tion 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 



FIG. 78 -Diagram representing a section O f the Septum is again 

 through the heart from base to apex. 



incompletely divided 



transversely, into a thinner basal portion into which veins 

 open, known as the auricle, and a thicker apical por- 

 tion from which arteries arise, called the ventricle. The 

 heart thus consists of a right auricle and ventricle and a 



