THE PERICARDIUM. 503 



organ is distended by injection, it often occupies the whole cavity 

 of the pericardium. 



The attachment of the pericardium to the diaphragm, is 

 exactly over the cordiform tendon of the latter. The French 

 anatomists have erroneously considered the fibrous layer of the 

 pericardium, as a mere reflection of the tendon upwards. By 

 separating them with a knife, we find, they are united by a 

 short cellular tissue, which is densest and strongest at the peri- 

 phery of their junction. The sides of the pericardium are 

 covered in part by the pleura, which gives the sac the appear- 

 ance of being formed by three tunics. 



Underneath the pleural lining, is found the phrenic nerve, 

 and in fat subjects, a good deal of adipose matter. 



The pericardium is composed of two lamina, the internal of 

 which covers the heart, as has been already described ; while 

 the external merely extends over the loose portion of the other, 

 and blends itself with the mediastinum, where that membrane 

 invests the great vessels. 



Its principal attachment or termination above, is upon the 

 arteries and veins entering the heart, (with the exception of the 

 vena cava inferior,) over which it sends tubular prolongations, 

 which gradually blend with their external coats. Between these 

 prolongations on the inside of the sac, hollow pouches are 

 necessarily left, which are called the cornua of the pericardium. 

 The fibrous layer of the pericardium resembles in structure 

 and appearance, the dura mater of the brain. 

 The arteries of the pericardium are very small ; they are de- 

 rived from the phrenic, bronchial, cesophageal, internal mam- 

 mary arteries, and from the aorta itself. Its veins terminate in 

 the vena azygos. Its nerves are few and small, and originate 

 from the cardiac plexus. - 



The internal surface of the pericardium is very smooth and 

 polished ; and in the living subject is constantly moistened with 

 a fluid which is probably effused from the exhalent vessels on 

 its surface. 



The quantity of this fluid does not commonly exceed two 

 drachms ; but in cases of disease it sometimes amounts to 



