TOPOGRAPHY OF THE THORAX AND ABDOMEN 23 



tilage and intercostal space it covers the anterior two- 

 thirds of this side of the heart (Plate XI). The superior 

 and middle lobes of the right lung together cover an area 

 which corresponds very closely to that covered by the su- 

 perior lobe of the left lung. The inferior lobe of each 

 lung comes into contact with the posterior part of the left 

 auricle near the disc between the sixth and seventh thoracic 

 vertebrae. The surface of each of these lobes in contact 

 with the heart becomes larger and larger from above down- 

 ward. This is especially true of the left side where the 

 heart encroaches more and more upon the internal surface 

 of this lung (Plates XI and XII). The right phrenic nerve 

 is in relation, in the superior mediastinum, with the superior 

 lobe. About the level of the third costal cartilage it crosses 

 the horizontal fissure and comes into relation with the mid- 

 dle lobe, which it crosses obliquely to reach the inferior 

 lobe near the level of the fourth costal cartilage. It re- 

 mains in contact with the inferior lobe down to its entrance 

 into the diaphragm. The left phrenic is only in contact 

 with the superior lobe of the left lung. 



The base of each lung is deeply concave in all direc- 

 tions as may be seen from the height to which the dome 

 of the diaphragm rises above the inferior margin of eacK 

 lung (Plates XXVIII to XXXV). Its margin (marge in- 

 ferior) is thin except internally, where it rests upon the cen- 

 tral tendon of the diaphragm. The anterior part of the 

 inferior margin of each lung is in the fifth intercostal space 

 at the level of the xiphosternal articulation and the disc 

 between the ninth and tenth thoracic vertebrae. The in- 

 ferior margin of the right lung is nearly in a hori- 

 zontal plane. It is behind the sixth right sterno- 

 chondral articulation at the sternum, in the fifth intercostal 



