I8 5 8 



HUMAN ANATOMY. 



1582 



. 



most importance to the course of the main bronchus : "On the posterior wall the 

 course of the left bronchus is from a point to the right of the fourth thoracic spine to 

 a point on the eighth rib three inches to the left of the spine. The course of the 

 right bronchus is from the same point above to a point on the eighth rib two inches 

 to the right of the spine. On the anterior wall the course of the left bronchus is from 

 the lower part of the second right sterno-chondral articulation to a point on the fifth 

 rib just internal to the mammillary, and of the right bronchus from the same point 

 above to the intersection of the fifth rib with the parasternal line. ' ' The hilum is 

 opposite the bodies of the sixth and seventh thoracic vertebrae and a part of the 

 adjacent ones. (Figs. 1569 and 1570. ) 



(The changes of the relations of the lungs during growth and in old age are 

 considered with those of the pleurae. ) 



THE PLEURAE. 



The pleurae are a pair of serous membranes disposed one over each lung and then 

 reflected so as to line the walls of the cavity containing it, thus forming a distinct 

 closed sac about each lung ; hence the pleura is divided into a visceral and a. parietal 

 layer. The latter is subdivided according to its situation into a mediastinal, a costal, 



a cervical, and a diaphragmatic part. 

 The visceral layer closely invests the 

 lung, following the surface into the 

 depth of the fissures. It leaves the 

 lung at the borders of the hilum and 

 invests the root for a short distance 

 (1-2 cm.), when it leaves the latter 

 and spreads out as the mediastinal 

 pleura, which is applied, back to 

 back, to the pericardium, thus form- 

 ing on each side a vertical antero- 

 posterior septum between the lungs 

 and the contents of the mediastina. 

 The prolongation over the root is not 

 quite tubular, since a triangular fron- 

 tal fold extends from beneath the root 

 to the inner side of the lung, growing 

 narrower as it descends, to end at or 

 near the lower borders. This is the 

 broad ligament of the lung ( ligamcn- 

 tum latuin pulmonis). Its line of at- 

 tachment to the lung often slants 

 backward. The mediastinal pleura, 

 besides being applied to the side of 

 the pericardium, lies also against some 

 of the structures of the other medi- 

 astina. Above it is in contact with the 

 thymus on both sides, the superior 

 vena cava on the right and the arch 

 of the aorta on the left. The phrenic 

 nerve descends on each side hetuccn 

 it and tin- pericardium in front of the 

 root of the lung. In the posterior 

 mediastinum K lies against th,- 1,-ft side of the descending aorta and the right of the 

 iippt-r part ..i ih,- greater azros vein. It is in contact with nearl the- whole oi the 





-tin, u, .11. showing relation-, of 

 n,| IMIIK (u-d) (<. tlu.nuic wall: lateral 



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.. I " llll *'*-t.liyLHV.> l llV71V^WlLII 



ophagus on th,- r . K ht, an.l ,usl before tin- latter passes through the diaphragm o 



ft also. It .-overs tin- ganfftiated cord of the sympathetic on bothades as i 



a -HO die <**talflcuro t and is here stretched so ti^tly across the termination 



n.e,v,,M al veins as to keep their ua lls distt-nded. Anteriorly it crosses the 

 treol.u tissue oi the anterior mediastinum below the remnants of the thymus. I 



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