756 



THE THORAX. 



The pericardium is a fibro-serous membrane, and consists, therefore, of two 

 layers ; an external fibrous, and an internal serous. 



The fibrous layer is a strong, dense membrane. Above, it surrounds the great 

 vessels arising from the base of the heart, on which it is continued in the form 

 of tubular prolongations, which are gradually lost upon their external coats ; 

 the strongest being that which incloses the aorta. The pericardium may be 

 traced, over these vessels, to become continuous with the deep layer of the 

 cervical fascia. Below, it is attached to the central tendon of the Diaphragm ; 

 and, on the left side, to its muscular fibres. 



The vessels receiving fibrous prolongations from this membrane are the aorta, 

 the superior vena cava, and the pulmonary arteries and veins. As the inferior 



Fig. 418. Front View of*the Thorax. The Ribs and Sternum are represented in Relation to 

 the Lungs, Heart, and other Internal Organs. 



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 a parietal portion. 

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

 vessels, to the extent of two inches 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 incloses the aorta 

 and pulmonary artery in a single tube ; but it only partially covers the superior 



