2^0 



THE PERICARDIUM. 



distance along them in the form of tnbular prolongations, which become 

 trradually lost upon their external coats. The superior vena cava, the 

 four pulmonary veins, the aorta, and the ri.i^dit and left divisions of 

 the pulmonary artery, in all eiglit vessels, receive investments of this 

 kind. 



1G3. 



Fig. 1G3. — Transverse Section' ok the Ciiest of a F(etus, illustratinu the kelativr 



POSITION OF THE HeART AND LuNGS AND THE INFLECTIONS OP THE PERICARDIUM 



AND Pleura (Allen Thomson after Luschka). 



The sketch represents the upper surface of the lower section ; the division is caiTied 

 nearly in a horizontal i^laue on a level with the interval in front between the fifth and 

 sixth ribs, s, the sternum ; c, the body of the seventh dorsal vertebx-a ; /(, the riglit, 

 and A', the left venti-icle ; cc, the ossophagus ; p n, the left pneumogastric nerve ; near 

 these letters respectively, the root of the right and left lungs ; the right pneumogastric 

 nerve is behind the cesojihagus ; a, the aorta ; v a, the vena azygos ; d, thoracic duct ; 

 1, the cardiac pcricai'dium ; 2, in the anterior mediastinal space, the parietal pericar- 

 dium ; 2', the cavity of the pericardium ; 3, the pulmonary pleuras passing over the 

 surface, and i-eflected at the roots of the kings ; 3', their cavity, and on the right side, 

 the reflection at the mcdiastiniim to the surface of the pericardium ; 4, the parietal or 

 costal pleuriu ; c, c, the walls of the chest inclosing the ribs, pectoral muscles, &c. 



The serous layer not only lines the fibrous layer of the pericardium, 

 but, like other serous membranes, is reflected on the surface of tlie 

 viscus Avhich it invests. It has, therefore, a visceral and a parietal 

 portion. The parietal portion adheres firmly to the fibrous mem- 

 brane, and becomes continuous with the visceral portion upon the 

 arch of the aorta and other great vessels, about 2 or 2} inches from 

 the base of the heart. In passing round the aorta and puhnonary 

 artery, it encloses those vessels in a common short tubular sheath 



