STRUCTURE OF PERICARDIUM. 311 



cardiac branch of the left vagus ; of the two, the last is the smaller, and 

 on the right of the other. 



The cardiac nerves from the left vagus and sympathetic are to be pur- 

 sued onwards to a small plexus (superficial cardiac) in the concavity of 

 the aorta. An offset of the plexus is to be traced downwards between the 

 pulmonary artery and the aorta towards the anterior coronary artery of 

 the heart ; and another prolongation is to be found coming forwards from 

 the deep cardiac to the superficial plexus : this dissection is difficult, and 

 will require care. 



When the pericardium is afterwards opened the nerves will be followed 

 on the heart. Oftentimes these small nerve^ are destroyed in injecting 

 the body. 



The pericardium is larger than the viscus it contains. Somewhat 

 conical in form, the wider part of the bag is turned towards the 

 diaphragm, and the narrower part upwards to the large vessels of the 

 heart. 



Occupying the iriterpleural space, it is situate behind the sternum, and 

 projects below on each side of that bone, but much more towards the left 

 than the right side. Laterally the pericardium is covered by the pleura, 

 and the phrenic nerve and vessels lie in contact with it. Its anterior and 

 posterior surfaces correspond with the objects in the interpleural space ; 

 and on the anterior aspect the bag is partly covered by the margin of the 

 lungs, especially the left. 



The heart-case consists of a fibrous structure, which is lined internally 

 by a serous membrane. 



The fibrous part surrounds the heart entirely, and is pierced by the dif- 

 ferent vessels of that organ : it gives prolongations around the vessels, and 

 the strongest of these sheaths is on the aorta. Inferiorly it is united by 

 fibres to the central tendon of the diaphragm. 



This membrane is thickest at the upper part, and is formed of fibres 

 crossing in different directions, many being longitudinal. When the peri- 

 cardium has been cut open, the serous lining will be discernible. 



The serous sac lines the interior of the fibrous pericardium, and is re- 

 flected over the surface of the heart. Like other serous membranes, the 

 arachnoid for example, it has a parietal and a visceral* part. After lining 

 the interior of the fibrous case, to which it gives the shining appearance, 

 the membrane is conducted to the surface of the heart by the different 

 vessels. As it is reflected on the aorta and the pulmonary artery it con- 

 tains those vessels in one tube, not passing between their contiguous sur- 

 faces ; and at the posterior part of the pericardium it forms a pouch 

 between the pulmonary veins of opposite sides. 



In front of the root of the left lung the serous layer forms a vertical 

 band, the cestigial fold of the pericardium (Marshal), which includes the 

 remains of the left innominate vein of the foetus. On separating the pul- 

 monary artery and bronchus, the band will be better seen. 



The vessels of the pericardium are derived from the aorta, the internal 

 mammary, the bronchial, the oesophageal, and the phrenic arteries. 



Nerves. According to Luschka the pericardium receives nerves from 

 the phrenic, sympathetic, and right vagus. 



