INFLECTIONS OF THE PLEURJE. 



893 



tinal partition, and are reflected each upon the root and over the entire free 

 surface of the corresponding lung. 



Each pleura consists of a visceral and a parietal portion : the visceral 

 portion, pleura pulmonalis, covers the lung ; and the parietal portion lines 

 the ribs and intercostal spaces, pleura costales, covers the upper convex 

 surface of the diaphragm, enters into the formation of the mediastinum, and 

 is reflected on the sides of the pericardium. 



The mediastinum, or partition between the two pleural cavities, is formed 

 by the reflection of each pleura from the anterior wall of the chest back- 

 wards on the pericardium to the root of the lung, and from the back of the 

 root of the lung to the vertebral column. Its division into anterior, middle, 



Fig. 626. TRANSVERSE SECTION OP THE CHEST OF A FCETUS, ILLUSTRATING THE INFLEC- 

 TIONS OF THE PERICARDIUM AND PLEURJS (after Luschka and from nature). 



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

 nearly in a horizontal plane on a level with the interval in front between the fifth and 

 sixth ribs, s, the sternum ; c, the body of the seventh dorsal vertebra ; A, the right, 

 and A', the left ventricle ; ce, the cesophagus ; 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 cesophagus ; a, the aorta ; v a, the vena azygos ; d, thoracic duct ; 

 1, the cardiac pericardium ; 2, the external pericardium ; 2', the cavity of the peri- 

 cardium ; 3, the pulmonary pleura passing over the surface, and reflected at the roots 

 of the lungs ; 3', their cavity, and on the right side, the reflection at the mediastinum to 

 the surface of the pericardium ; 4, the external or costal pleurae ; c, c, the walls of the 

 chest inclosing the ribs, pectoral muscles, &c. 



and posterior mediasiina, and the position and contents of each, have been 

 already described (p. 297). 



