714 



HUMAN ANATOMY. 



The same incision — or an extension downward of this one — will permit of suffi- 

 cient exposure of the heart for cardiac massage, a method of resuscitation in des- 

 perate cases of syncope during anaesthesia which has been recently employed, but 

 the value of which, if it has any, cannot now be estimated. 



THE PERICARDIUM. > 



The pericardium is the serous sac which encloses the heart and the proximal por- 

 tions of the great vessels. Like other serous sacs, it consists of two layers, one of 

 which, the visceral layer, closely invests the heart and at its base becomes continuous 

 with the parietal layer, within which it is invaginated. 



The visceral layer, sometimes termed the epicardium, is an exceedingly thin 

 membrane, and is throughout the greater part of its extent so closely adherent to the 

 outer surface of the heart that any attempt to detach it results in injury to the super- 

 ficial layers of the heart musculature. Over the right side and the anterior surface 

 of the ventricular portion of the heart, however, a certain amount of fat, even in thin 

 persons, occurs between the muscular tissue and the epicardium. 



Fig. 675. 



Sternum 



Right ventricle 



Pericardial sac 



Interventric- 

 ular septum 



Lung 

 Parietal 

 pericardium 

 Visceral 

 ■;,■' /'• >'  \ peiicardium 



^ ',<<*; ' '. — Pleura 



. '.•■'■ t 



*'j?t^ Right auriculo- 



ventricular valve 



Eustachian valve 



Inferior vena cava 



CEsophagus 



'^— Vena azj'gos 



— VIII. thoracic vertebra 



Thoracic aorta' 



Portion of cross-section of tjody at level of eighth thoracic vertebra, viewed from above, 

 showing heart enclosed by pericardium. 



The parietal layer, much stronger than the visceral, forms a somewhat 

 conical sac, the base of which rests upon and is attached to the diaphragm, while its 

 apex surrounds the roots of the aortae. Notwithstanding its greater size, no cavity 

 exists normally between this and the visceral layer, the two being in contact 

 throughout, e.xcept below, where, towards the periphery of the base of the parietal 

 cone, a slight space occurs which is normally occupied by a quantity of pericardial 

 flu id ( liquor pericardii) . 



At the sides, and to a considerable extent on its a?iterior surface, the parietal 

 layer of the pericardium is united to or is in close contact with the adjacent pleurae. 

 At the upper part of its anterior surface where it covers the aorta it is free from such 

 contact, and over a triangular area near the base of the cone the anterior surface 

 rests upon the posterior surface of the lower part of the sternum, to which it is 

 united by soine loose areolar tissue. Posteriorly it is free to a considerable extent 

 from the pleurae, that portion of it which covers the posterior surface of the left 

 auricle resting upon the oesophagus and the thoracic aorta. The base of the cone 

 is firmly united to the upper surface of the diaphragm throughout its entire extent, 

 the area of attachment corresponding to the anterior and a portion of the left lobe of 

 the central tendon. 



