THK THORAX. 4C5 



In.lt 'prudently of these four serous layers, the right pleura furnishes a 

 special membranous fold, which arises from the inferior wall of the thoracic 

 cavity, and ascends to envelop the posterior vena cava. This fold also 

 sustains the right diaphragmatic nerve. 



In order to study the various portions of the pleurto collectively, with 

 their reciprocal relations, and their connections with the organs contained 

 in the thoracic cavity, we will suppose three transverse sections of this 

 cavity: one passing behind the heart; the other at the roots of the lungs, 

 and dividing the left ventricle of the heart ; the third traversing the anterior 

 mediastinum, a little in front of the right ventricle. 



If, in the first section (Fig. 235), wo take the costal pleura at the point 

 a, and follow it up to 6, we will see it folded downwards to form the 



Fig. 235. 



' _ ;;. 



Vie. 237. 



TllKii!:! IK'M 



or nil. THORACIC CAVITY; IN TKN I >F.I> TO SHOW TIIK 

 MSI-.KI | l\ en Illl I'l.I.nt.K. 



mediastinal layer, to be applied to the aorta, r, and the a-sophagus, </ , thin 

 reflected ut con the lung,/, enveloping every part of the organ ; returning to 

 the jMnnt e, it leaves the lung, is again reflected to achieve (he formation 

 of the mediastinal septum, b g, and finally regains the point it started from. 

 On the right side, with only a slight variation, it lias the same arrangement. 

 After iKiing carried from the point a' to />', then to ', and after enveloping 

 the lint'.', returning to ', :ind being reflected in the median plane to the 

 point </, the right pleura leaves the inferior thoracic wall to pass around 

 tin posterior vena cava, and come hack t.> //'. its point of departure. 



The second section, (represented by Fig. 236) shows the pleura airivl 

 at the point b, descending on the root of the lung. .-. covering that organ 

 aii'l returning to c, and reflected on the pericardium, //, to gain the jx>int n. 



In the third section (Fig. 237), we see the parietal pleura, a b, without 

 any points of continuity with the visceral pleura, c. It is at the lev. 1 of 

 this section that the lung forms two perfectly free loins, which am not 

 attached to the anterior mediastinum. 



STRUCTURE. Like all the serous membranes, the pleurre have a free faco 



covered by a simple tesselated epithelium; it is perfectly smooth, always in 



contact with itself, and constantly lubricated by a serous fluid which 



total lli; gliding of the lung on the pari.-i, s of the thonu-ic cavity 



