34 2 



THE RESPIRATORY SYSTEM 



(2) the mediastinal pleura, which covers the great vessels, etc. ; 



(3) the diaphragmatic pleura, which covers the upper surface 

 of the diaphragm ; (4) the cupula pleura, which projects 

 upwards into the neck in association with the apex of the 

 lung. The pulmonary and parietal pleurae become continuous 

 with one another at the root of the lung (Fig. 123). 



When a transverse section through the thorax above the 

 level of the root of the lung is examined, it is found that there 

 is no continuity between the parietal and the pulmonary 

 pleurae. The costal pleura lines the inner surfaces of the ribs 



FIG. 122. Diagram of a Transverse Section through the Thorax 

 above the level of the root of the lung, showing the arrange- 

 ment of the parietal and visceral layers of the pleura. 



and passes medially on the posterior surface of the sternum to 

 the median plane. It there becomes continuous with the 

 mediastinal pleura, which passes backwards over the great 

 vessels, etc., to reach the vertebral column. At the sides of 

 the bodies of the vertebrae, the mediastinal pleura passes 

 laterally on to the ribs (Fig. 122). 



When a section through the thorax at the level of the root 

 of the lung is examined, the arrangement is found to be very 

 similar in regard to the costal pleura, but, as the mediastinal 

 pleura passes backwards from the sternum, it comes into con- 

 tact with the pericardium. From the pericardium the pleura 

 is carried laterally on the anterior surface of the root of the 



