84 ANATOMY FOR NURSES. [CHAP. VIII. 



The pericardium forms a completely closed sac ; its internal 

 surfaces are very smooth and polished, they are lined by epithe- 

 lium, and secrete a small quantity of serous fluid. As their 

 opposing surfaces, owing to the constant contractions of the 

 heart, are continually sliding one upon the other, they are ad- 

 mirably constructed to protect the heart from any loss of power 

 by friction. 



The interior of the heart is lined by a delicate, smooth mem- 

 brane, called the endocardium. This pavement membrane lines 

 all the cavities of the heart, and is continued into the blood- 

 vessels, forming their innermost coat. 



The cavities of the heart. The heart is divided from the base 

 to the apex, by a fixed partition, into a right and left half. 



The two sides of the heart 

 have no communication with 

 each other: the right side al- 

 ways contains venous, and the 

 left side arterial, blood. Each 

 half is subdivided into two 

 cavities, the upper, called au- 

 ricle ; the lower, ventricle. 

 These cavities communicate 

 with one another by means of 

 constricted openings, the auric- 

 ulo-ventricular orifices, which 

 are strengthened by fibrous 

 FIG. 65. -RIGHT 'SIDE OF HEA^ i, rings, and protected and guard- 



cavity of right auricle ; 3, vena cava supe- ed by valves. The valve guard- 



rior; 4, vena cava inferior; 9, entrance of , i j i , 



auriculo-ventricular opening ;, right ven- m g the n g ht aunculo,ventriC- 



tricle; 6, c, cavity of right ventricle, on ular opening is Composed of 



the walls of which the columnse carnse ,-t , -, n , . 



are seen; d, pulmonary artery; e, /, tri- three triangular flaps, and IS 



cuspid valve; z,columnae carnse; m, semi- hence named tricuspid. The 



lunar val ve ; o, left ventricle; p, ascending n . , ~ 



aorta; q, arch; r, descending aorta. na P s are mainly formed of 



fibrous tissue covered by endo- 

 cardium. At their bases they are continuous with one another, 

 and form a ring-shaped membrane around the margin of the auric- 

 ular opening : their pointed ends are directed downwards, and 

 are attached by cords, the chordce tendinece, to little muscular 

 pillars provided in the interior of the ventricles for this purpose. 

 The valve guarding the left auricular opening consists of only 



