THE THORAX 9yj 



At the level of the manubrium sterni the pleura passes uninterrup- 

 tedly backwards to the vertebral column. That of the right side 

 passes over the side of the superior vena cava, innominate artery, 

 right innominate vein, and trachea ; whilst that of the left side passes 

 over the side of the left common carotid and left subclavian arteries, 

 oesophagus, and thoracic duct. The two pleurae, as they pass back- 

 wards at this level, form the lateral boundaries of the space which 

 is called the superior mediastinum. 



Below the level of the root of the lung the aatero-posterior reflec- 

 tion of the pleura is complicated by a triangular fold, called the 

 ligamentum latum pulmonis. This fold consists of two layers of 

 pleura, in close apposition, which are continuous superiorly with 

 the anterior and posterior pleural investments of the root of the 

 lung. It extends, on the one hand, between the lower border of the 

 root of the lung and the diaphragm, to which latter it is aiiached, 

 and, on the other hand, between the pericardium and the inner 

 surface of the lung below the level of the root. In the last-named 

 situation its two layers separate, to encase the lung at that level. 

 Its lower border is free and concave. 



(2) In the vertical direction. — Superiorly the parietal pleura of each 

 side rises, in the form of a dome, into the root of the neck for about 

 I inch above the clavicle, where it is covered by Sibson's fascia. 

 This fascia is attached, on the one hand, to the internal border of 

 the first rib, and, on the other, to the front of the transverse 

 process of the seventh cervical vertebra. The subclavian artery 

 and innominate vein are intimately related to the dome of the 

 pleura internally and anteriorly, the artery being the higher of the 

 two. Inferiorly the parietal pleura of each side is reflected from 

 the thoracic wall on to the upper surface of the corresponding 

 portion of the diaphragm, which it covers where the base of the lung 

 rests upon it. The intervening portion of the diaphragm (central 

 tendon) is covered by the serous portion of the pericardium. In- 

 ternally the diaphragmatic pleura becomes continuous with the 

 mediastinal pleura. 



Lines of Reflection of the Pleurae — Sternal Reflection. — Behind 

 the manubrium sterni the right and left pleurae are separated from 

 each other by an interspace which represents the superior medi- 

 astinum. At the levd of the junction of the manubrium and body 

 of the sternum they meet each other, and descend behind the body 

 of the bone, in close contact and inclining slightly to the left of the 

 median line. At the level of the lower border of the fourth costal 

 cartilage the left pleura parts company with the right, and passes 

 outwards and downwards close to the left border of the sternum, 

 and in intimate relation with the pericardium. There is, however, 

 a small triangular area of that sac which is uncovered by the pleura, 

 and lies in direct relation to the anterior thoracic wall. The left 

 pleura continues its downward course as far as the inner surface of 

 the sixth costal cartilage, lying not far from the left border of the 

 sternum. At this level it again passes outwards and downwards, 



