1236 



THE RESPIRATORY SYSTEM 



THE PLEURA 



The pleura (fig. 993) is a closed serous sac, which invests the luug (pulmonary 

 pleura), and lines the inner surface of the thoracic walls (parietal pleura). The 

 pleural cavity [cavum pleurse] is the capillary space enclosed by the walls of the sac 

 containing a little fluid which lubricates the apposed surfaces of the pulmonary 

 and parietal membranes. There are two pleurse, one in relation to each lung, 

 completely separated by a sagittal partition, the mediastinum. 



Fig. 999. — Pleural Cavity Opened From in Front. 

 1, first rib; 2, manubrium sterni; 3, acromial extremity of clavicle; 4, xiphoid process, 

 5, linea alba; 6, m. transversus abdominis; 7, seventh rib; 8, sternocleidomastoid m.; 9, 

 anterior scalene m.; 10, larynx; 11, thyreoid gland; 12, deep layer of cervical fascia in front 

 of the trachea; 13, corresponds to upper part of anterior mediastinal cave; 14, pleural cupola; 

 15, mediastinal pleura; 16, lower margin of costal pleura; 17, pericardium; 18, superior lobe 

 of lung; 19, middle lobe of right lung; 20, inferior lobe of lung; 21, diaphragm. (Rauber- 

 Kopsch.) 



The pulmonary pleura [pleura pulmonalis] forms a smooth glistening coat over 

 the outer surface of the lung, with the tissue of which it is inseparably connected. 

 At the hilus the pulmonary pleura passes from the mediastinal surface of the lung 

 to cover the root above, in front, and ])ehind, and becomes continuous medialward 

 with the parietal pleura of the mediastinum. Below the root of the lung the 

 pleiu-a is reflected rnediahvard in a double layer as the pulmonary ligament 

 [lig. pulmonale] (fig. 994). 



This presents anterior and posterior surfaces and three margins; the base is mostly free, and 

 directed toward the diaphragm, with wliich it, is connected at its medial end; the apex is at the 

 lung root, one margin is next to the hmg, and the other joins the mediastinal pleura. 



