88 ANATOMY AND PHYSIOLOGY FOR NURSES 



left than the right side of the thorax, its base pointing up- 

 ward and its apex downward toward the left side. It is 

 a strong body, being made up of involuntary muscular 

 tissue, which is known as the myocardium. It is enclosed 

 in the pericardium, a loose sac that also contains a serous 

 lubricating fluid. The heart is commonly regarded as the 

 starting-point of the blood in its course through the body ; 

 from this point the blood is propelled, through the arteries, 

 to every part of the system. 



FlG. 45- Orifices of the heart, seen from above, both the auricles and 

 the great vessels being removed: PA, Pulmonary artery and its semilunar 

 valves ; Ao, aorta and its valves ; RA V, tricuspid, and LA V, bicuspid 

 valves; mv, segments of mitral valve; Iv, segment of tricuspid valve 

 (Huxley). 



Cavities of the Heart. The heart is divided into 

 two parts the right and the left heart. These are fur- 

 ther divided into four distinct cavities, called respectively 

 the right and the left ventricle and the right and the left 

 auricle. By referring to the illustration (Fig. 48) it will 

 be seen that the auricles are the upper cavities and the 

 ventricles the lower. 



The cavities of the heart are lined by a delicate, smooth 

 membrane, the endocardium, which is continuous with the 

 intima or innermost coat of the great blood-vessels. 



