THE PERICARDIUM. 



1085 



The >'./></. layer invests the heart, and is then reflected on the inner surface 

 of the pericardium. It consists, therefore, of a visceral and parietal portion. 

 The former invests the surface of the heart and the commencement of the great 

 vessels to the extent of one inch and a half from their origin ; from these it is 

 reflected upon the inner surface of the fibrous layer. The serous membrane 

 encloses the aorta and pulmonary artery in a single tube ; hence between these 

 Is and the auricles posteriorly is a passage, the transverse pericardial sinus ; 

 but it only partially covers the superior and inferior vena cava and the four pul- 



Lffl subdarian art. 

 Sight pulmonary art. 



Right 

 subdavian 

 Left comm. 

 carotid artery. 



FIG. 693. Pericardium, from behind. (From the same preparation as the preceding figure.) 



monary veins. Its inner surface is smooth and glistening, and secretes a thin 

 fluid which serves to facilitate the movements of the heart. 



Arteries <>f the Pericardium. These are derived from the internal mammary 

 and its umsculo-phrenic branch and from the descending thoracic aorta. 



^\- rces of the Pericardium. These are branches from the vagus, the phrenic, 

 and the sympathetic. 



The Vestigial Foil of the Pericardium. AYhen the pericardium is opened 

 there is seen lying between the left pulmonary artery and subjacent pulmonary 

 vein a triangular fold (vestigial fold of Marshall) of the serous layer, which encloses 

 between its layers the remains, a fibrous cord, of the left superior vena cava. This 

 cord may sometimes be traced upward to the left superior intercostal vein. 



