502 THE PERICARDIUM. 



CHAPTER XVI. 



- 



OF THE HEART AND PERICARDIUM, AND THE GREAT VESSELS 

 CONNECTED WITH THE HEART. 



Of the Pericardium. 



THE heart is enclosed by a membranous sac, which, upon a 

 superficial view, seems only connected with its great vessels. 



The whole of the organ lays unattached in the cavity of 

 the sac, except, by the arteries and veins connected with its 

 base. The sac is in fact composed of two layers, one external 

 and fibrous, and one internal and serous ; the latter of these not 

 only lines the inner face of the outer membrane, but is reflected 

 like other serous membranes, over the roots of the vessels 

 placed in the pericardium, and over the whole of the outer sur- 

 face of the heart itself. This internal serous lining is very thin 

 and delicate, and can only be raised in small shreds, either 

 rom the outer layer of the pericardium, or from the heart ; 

 except at the base of the latter organ, where, in females, it is 

 usually, and in males, frequently, separated from the muscular 

 tissue, by some sub-serous fatty matter. 



If it were dissected from the heart, without laceration or 

 wounding, it would be an entire sac. 



The pericardium, thus arranged, is placed between the two 

 lamina of the mediastinum, and adheres firmly to them where 

 they are contiguous to it ; it also adheres firmly to the dia- 

 phragm below, and thus preserves the heart in its proper 

 position. 



The figure of the pericardium, when it is distended, is some- 

 what conical ; the base being on the diaphragm. The cavity 

 formed by it is larger than the heart after death, but it is 

 probable, that the heart nearly fills it during life ; for when this 



