THE PLEURAL MEMBRANES. 929 
mediastinal pleura is applied to the arch of the aorta and the phrenic and vagus 
nerves; to the left innominate vein, the left superior intercostal vein, and the left 
common carotid and left subclavian arteries; to the cesophagus and the thoracic 
duct. The right mediastinal pleura, 
on the other hand, is applied, above 
the level of the root of the lung, 
to the upper part of the vena cava 
and right innominate vein; to the 
right innominate artery; to the 
vena azygos major, as it hooks 
forwards above the bronchus; to 
the vagus and phrenic nerves; and 
to the right side of the trachea. 
Opposite the root of the lung, 
as well as in the region below it, 
the mediastinal pleura clothes the 
corresponding aspect of the peri- 
eardium, and is somewhat firmly 
attached to it. As the phrenic 
nerve passes downwards upon the 
pericardium it is likewise covered 
over by the pleura. In the region 
corresponding to the upper lateral 
aspect of the pericardium the 
mediastinal pleura is prolonged 
outwards, so as to form an invest- 
ment for the root of the lung, and 
become continuous around the 
hilus of the lung with the visceral 
pleura. Below the root of the 
lung the two layers of pleura which 
invest it come into apposition with 
each other,and are prolonged down- 
wards as a distinct fold, termed 
the ligamentum latum pulmonis. 
This fold stretches between the 
pericardium and the lower part of 
the inner surface of the lung, and 
ends below in a free border. 
Behind the root of the lung 
and the ligamentum latum pul- 
monis the mediastinal pleura on 
the right side is carried backwards 
to the vertebral column on the Fic. 629.—LATERAL VIEW OF THE RIGHT PLEURAL SAC IN 
cesophagus ; whilst on the eft side A SUBJECT HARDENED BY FORMALIN-INJECTION. The 
it is carried backwards over the blue lines indicate the outline of the right lung, and also 
: the position of its fissures. 
descending aorta, and to a small Ey wae gs ey 
extent, in the region immediately above the diaphragm and in front of the aorta, 
over the lower end of the cesophagus. 
Lines of Pleural Reflection.—These are three in number—viz. the anterior or 
sternal, the posterior or vertebral, and the lower or diaphragmatic. The pleural cavities 
are not symmetrical. The left is longer and narrower than the right, and it thus happens 
that the lines of pleural reflection do not accurately correspond on the two sides of the 
body. Further, although the posterior line of reflection is fairly constant, the other two 
reflection-lines are subject to marked variations in different subjects. Consequently the 
following description must be regarded as merely giving the average condition. 
The “posterior or vertebral line of pleural reflection is that along which the costal pleura 
turns forwards from the vertebral column so as to become the mediastinal pleura. On 
the right side, above the root of the lung, the pleura passes from the bodies of the vertebra 
59 
