164 



ANATOMY FOR NURSES 



[Chap. X 



ity ; P. P. parietal portion of pericardium ; 

 V.P. visceral portion. 



(2) The internal or serous portion of the pericardium is a 

 completely closed sac ; it envelops the heart and lines the fibrous 

 pericardium. The heart, however, is not within the cavity of 

 the closed sac. (See Fig. 100.) That portion of the serous 



pericardium which lines 

 and is closely adherent to 

 the heart is called the vis- 

 ceral portion (visais or- 

 gan) ; the remaining part 

 of the serous pericardium, 

 namely, that which lines 

 the fibrous pericardium, is 



Fig. 100. — Diagram of Heart and Se- knowu as the parietal por- 

 Rous Pericardium. In .4, heart and pcricar- .• / • U\ T*! 



dium lying separately. In B, pericardium lying tlOn {panes, H Wall). ilie 

 around heart. H, heart ; P. C. pericardial cav- cavity of the SCrOUS peri- 

 cardium contains a small 

 quantity of serous liquid. 

 Its contiguous or opposed surfaces are lined by endothelium and 

 are very smooth and polished. 



As the opposing surfaces, owing to the constant contractions 

 of the heart, are continually sliding one upon the other, they are 

 admirably constructed to protect the heart from any loss of power 

 by friction. 



Endocardium. — The interior of the heart is lined by a delicate, 

 smooth membrane, called the endocardium. This pavement 

 membrane (endothelium) 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, fre- 

 quently called right and left heart. The two sides of the heart have 

 no communication with each other after birth. The right always 

 contains venous, and the left side arterial, blood. Eaclr half is 

 subdivided into two cavities, the upper, called auricle (atrium) ; 

 the lower, ventricle (ventriculumj. If we examine these cavities, 

 we notice that the muscular walls of the auricles are much thinner 

 than those of the ventricles, and the wall of the left ventricle is 

 thicker than that of the right. This difference in bulk is to be 

 accounted for, as we shall see later on, by the greater amount of 

 work the ventricles, as compared with the auricles, have to do. 



