95 THE RESPIRATORY SYSTEM. 
on to the right side of the trachea; whilst below this level, and behind the peri- 
cardium, it passes from the vertebral bodies on to the @sophagus. On the /eft sede, and 
above the arch of the aorta the pleura along this line of reflection is carried from the 
vertebral column on to the cesophagus and thoracic duct ; below that level it passes on 
to the descending thoracic aorta. In the upper part of the chest the right and left 
lines of reflection are placed well apart from each other, and about equidistant from the 
mesial plane. As they are 
traced downwards they 
approach more closely to 
each other and deviate to 
the left, so that whilst the 
Parietal reflection on the right side 
Tatee takes place from the front 
aspect of the vertebral 
bodies, on the /eft sede it 
takes place from the left 
ae aspect of the vertebral 
arch column. This is due to 
the position of the descend- 
ing thoracic aorta. 
iumenay The anterior line of 
pleural refiection is that 
Bronchus along which the costal 
pleura leaves the anterior 
thoracic wall to become the 
Pulmonary Mediastinal pleura. The 
vein ' line differs somewhat on 
the two sides, and in both 
cases shows a tendency to 
(Esophagus Aeviate to the left(Fig. 628, 
p- 928). Behind the upper 
part of the manubrium 
sterni the two pleural sacs 
are separated from each 
other by an angular inter- 
val. The lines of reflection 
at the inlet of the thorax 
~Diaphragm correspond to the sterno- 
clavicular joimts. From 
these points, as they are 
traced downwards, they 
converge on the back of the 
manubrium, until at last 
they meet a short distance 
above the upper end of the 
gladiolus. Here the two 
sacs come into contact with 
each other, and the lines of 
reflection coincide. From 
this they proceed down- 
Fic, 630.—LxEFT PLEURAL Sac IN A SUBJECT HARDENED BY FORMALIN- wards on the back of the 
INJECTION, opened into by the removal of the costal part of the parietal 
pleura. The lung has also been removed so as to display the media- 
stinal pleura. 
(&sophagus 
Left subclavian artery 
\ 
Left common carotid artery. x f 
Left superior intercostal vein, 
Left innominate vein 
re) 
Parietal pleura (ent ed 
ardium 
Peric 
sternum, with a slight de- 
viation to the left of the 
mesial plane, until a point 
immediately above the level of the sternal attachments of the fourth costal cartilages is 
reached, and here the two sacs part company. The line of reflection of the right pleura is 
continued downwards in a straight line behind the sternum until the back of the ensiform 
cartilage is reached, and here the sternal reflection-line passes into the right diaphragmatic 
reflection-line. Opposite the stetnal attachment of the fourth costal cartilage the reflection- 
line of the left pleura deviates outwards on the back of the sternum, and is continued 
downwards at a variable distance from the right pleura. A small triangular area of 
pericardium is thus left uncovered by pleura, and therefore in direct contact with the 
anterior chest-wall. Leaving the sternum, the reflection-line of the left pleura descends 
