THE PERICARDIUM. 



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nary veins. As the inferior vena cava enters the pericardium through the central 

 tendon of the Diaphragm, it receives no covering from the fibrous layer. 



The serous 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 an inch and a half from their origin ; from these it is reflected 

 upon the inner surface of the fibrous layer, lining, below, the upper surface of the 

 central tendon of the Diaphragm. The serous membrane encloses the aorta and 

 pulmonary artery in a single tube, so that a passage, termed the transverse sinus 

 of the pericardium, exists between these vessels in front and the auricles behind. 



FIG. 275. Front view of the thorax. The ribs and sternum .are represented in relation to the lungs, heart, 

 and other internal organs. 1. Pulmonary orifice. 2. Aortic orifice. 3. Left auriculo- ventricular orifice. 4. Right 

 auriculo-ventrlcular orifice. 



The membrane only partially covers the superior vena cava and the four pulmonary 

 veins, and scarcely covers the inferior cava, as this vessel enters the heart almost 

 directly after it has passed through the Diaphragm. Its inner surface is smooth 

 and glistening, and secretes a serous fluid, which serves to facilitate the movements 

 of the heart. 



Arteries of the Pericardium. These are derived from the internal mammary 

 and its musculo-phrenic branch, and from the descending thoracic aorta. 



Nerves of the Pericardium. These are branches from the vagus, the phrenic, 

 and the sympathetic. 



The Vestigial Fold of the Pericardium. Between the left pulmonary artery and 

 subjacent pulmonary vein is a triangular fold of the serous pericardium ; it is known 



