I'LEURAL REFLECTION. 443 



Below the root of the lung it forms a thin fold, the ligamentum 

 lafiim pulmonis, which unites the inner surface of the lung to 

 the side of the pericardium, and may be seen by enlarging 

 the hole in the pleura and drawing the lower part of the lung 

 out. The ligament then appears as a fold passing from the broad liga- 

 inner part of the lung to the pericardium and presenting a free JJg* of the 

 lower border. At the upper part of the chest the pleura forms a 

 dome over the apex of the lung, which may be revealed by drawing 

 that part of the lung downwards. At this part the membrane is 

 strengthened by the strong fascia of the neck (Sibson's fascia), which Sibson's 

 is attached to the inner border of the first rib and closely invests faicia> 

 the vessels at the upper opening of the thorax. 



LINE OF PLEURAL REFLECTION. Surface marking. The pleura! Surface 

 cavity extends upwards on each side in the neck, two inches above markm s 

 the anterior part of the first rib, or an inch above the middle of the 

 clavicle, where the shoulder is depressed. From this point the 

 anterior limit of the sac extends downwards and outwards, reaching 

 the middle line at the lower part of the manubrium sterni, and 

 continues down in that line, or a little to the left thereof. 



On the left side, opposite the fourth costal cartilage, it passes left side > 

 outwards until clear of the sternum, and then passes downwards 

 along its left side to the back of the sixth costal cartilage, thus 

 presenting a notch, in which the pericardium comes into contact 

 with the lower part of the sternum ; but the notch is much less pracordial 

 than that formed by the corresponding part of the lung (fig. 162). nc 

 The pleura is connected by fascial bands to the upper surface of 

 the diaphragm, and the line of its reflection passes in succession 

 behind the sixth and seventh costal cartilages, reaching the junction 

 of the eighth rib, with its cartilage in the lateral line. From this 

 point it extends round the body, crossing the lower border of the 

 tenth rib in a line midway behind the vertebras behind and the 

 middle line in front. This is usually the lowest part of the pleura! 

 cavity, and from here it extends backwards to the inner surface of 

 the twelfth rib, and, quite commonly, it projects below the twelfth projection 

 rib under the external arched ligament of the diaphragm. It is twelfth rib 

 most important to bear this fact in mind in operations on the 

 posterior abdominal Avail, so as to avoid opening the pleura! sac. 



On the right side the line of the pleural reflection is the same as on right* 

 on the left, except that it does not present notch behind the S1 e> 

 sternum, where it overlaps the pericardium, but continues directly 

 downwards on the middle line until it reaches the seventh costal 

 cartilage, behind which its line of reflection passes outwards and 

 downwards as on the left side. 



THE MEDIASTINUM. The median thoracic partition, or medias- Along 

 timi.m, is formed by the inner portion of the parietal pleura on sacs f rma 

 each side, and the structures interposed between the two mem- se P tum - 

 branes. It extends the whole depth of the thorax, and reaches 

 mesially from the spine to the sternum, thus separating the right 

 and left pleural cavities. In the centre the two layers of serous 

 membrane are widely separated by the heart ; but in front and 



