SPLANCHNOLOGY 



in health they are in actual contact with one another, but the potential space 

 between them is known as the pleura! cavity. When the lung collapses or when 

 air or fluid collects between the two layers the cavity becomes apparent. The right 

 and left pleural sacs are entirely separate from one another; between them are all 

 the thoracic viscera except the lungs, and they only touch each other for a short 

 distance in front; opposite the second and third pieces of the sternum the interval 

 between the two sacs is termed the mediastinum. 



Different portions of the parietal pleura have received special names which 

 indicate their position: thus, that portion which lines the inner surfaces of the 

 ribs and Intercostales is the costal pleura; that clothing the convex surface of the 

 diaphragm is the diaphragmatic pleura; that which rises into the neck, over the 

 summit of the lung, is the cupula of the pleura (cervical pleura) ; and that which is 

 applied to the other thoracic viscera is the mediastinal pleura. 



Cardiac notch 

 Lower margin of lung 



Lower margin of -pleura 



Fia. 965. Front view of thorax, showing the relations of the pleurae and lungs to the chest wall. 

 Pleura in blue ; lungs in purple. 



Reflections of the Pleura (Figs. 965, 966). Commencing at the sternum, the 

 pleura passes lateralward, lines the inner surfaces of the costal cartilages, ribs, 

 and Intercostales, and at the back part of the thorax passes over the sympathetic 

 trunk and its branches, and is reflected upon the sides of the bodies of the verte- 

 brae, where it is separated by a narrow interval, the posterior mediastinum, from 

 the opposite pleura. From the vertebral column the pleura passes to the side of the 

 pericardium, which it covers to a slight extent; it then covers the back part of the 

 root of the lung, from the lower border of which a triangular sheet descends verti- 

 cally toward the diaphragm. This sheet is the posterior layer of a wide fold, 

 known as the pulmonary ligament. From the back of the lung root, the pleura 



