THE PLEURA 



1089 



Trachea 



R. subclavian art. 

 R. innominate vein 



may be traced over the costal surface of the lung, the apex and base, and also over 

 the sides of the fissures between the lobes, on to its mediastinal surface and the front 

 part of its root. It is continued from the lower margin of the root as the anterior 

 layer of the pulmonary ligament, and from this it is reflected on to the pericardium 

 (pericardial pleura), and from it to the back of the sternum. Above the level of 

 the root of the lung, however, the mediastinal pleura passes uninterruptedly from 

 the vertebral column to the sternum over the structures in the superior medias- 

 tinum. Below, it covers the upper surface of the diaphragm and extends, in 

 front,- as low as the costal cartilage of the seventh rib; at the side of the chest, 

 to the lower border of the tenth rib on the left side and to the upper border of the 

 same rib on the right side; and behind, it reaches as low as the twelfth rib, and some- 

 times even to the transverse process 

 of the first lumbar vertebra. Above, 

 its cupula projects through the 

 superior opening of the thorax into 

 the neck, extending from 2.5 to 5 

 cm. above the sternal end of the 

 first rib; this portion of the sac is 

 strengthened by a dome-like expan- 

 sion of fascia (Sibson's fascia), at- 

 tached in front to the inner border 

 of the first rib, and behind to the 

 anterior border of the transverse 

 process of the seventh cervical 

 vertebra. This is covered and 

 strengthened by a few spreading 

 muscular fibers derived from the 

 Scaleni. 



In the front of the chest, where 

 the parietal pleura is reflected back- 

 ward to the pericardium, the two 

 pleural sacs are in contact for a 

 short distance. At the upper part 

 of the chest, behind the manubrium, 

 they are separated by an angular 

 interval ; the line of reflection being 

 represented by a line drawn from 

 the sternoclavicular articulation to 

 the mid-point of the junction of 

 the manubrium with the body of the 

 sternum. From this point the two 

 pleurae descend in close contact to 



the level of the fourth costal cartilages, and the line of reflection on the right side 

 is continued downward in nearly a straight line to the xiphoid process, and then 

 turns lateralward, while on the left side the line of reflection diverges lateralward 

 and is continued downward, close to the left border of the sternum, as far as the 

 sixth costal cartilage. The inferior limit of the pleura is on a considerably lower 

 level than the corresponding limit of the lung, but does not extend to the attach- 

 ment of the diaphragm, so that below the line of reflection of the pleura from the 

 chest wall on to the diaphragm the latter is in direct contact with the rib cartilages 

 and the Intercostales interni. Moreover, in ordinary inspiration the thin inferior 

 margin of the lung does not extend as low as the line of the pleural reflection, with 

 the result that the costal and diaphragmatic pleurae are here in contact, the inter- 

 vening narrow slit being termed the phrenicocostal sinus. A similar condition 

 69 



Lower margin 



of pleura 

 Lower margin of lung 



U 



FIG. 966. Lateral view of thorax, showing the relations of 

 the pleurae and lungs to the chest wall. Pleura in blue; lungs io 

 purple. 



