22 UNIVERSITY OF MISSOURI STUDIES 



as usual, and becomes less and less distinct from above 

 dovirnward. The oesophagus which lies a little anterior to 

 these vessels is in contact with both lungs. It is partially 

 separated from the left lung above by the aorta, but below 

 where it crosses the anterior surface of the aorta it is in 

 direct contact with this lung (Plates IX, X, XI, and XII). 

 The lungs do not come into contact with the thoracic duct 

 since that vessel lies between the vena azygos major and the 

 aorta and behind the oesophagus. 



In the middle and anterior mediastinal regions the in- 

 ternal surfaces of the lungs are in contact with the heart. 

 When seen in anterior projection (Plates XXVIII and 

 XXXII)_ the anterior border of the right lung overlaps the 

 right border of the heart about 2 cm., while the anterior 

 border of the left lung overlaps the left border of the heart 

 less than 1 cm. at any point. All three lobes of the right 

 and both lobes of the left lung touch the heart. The su. 

 perior lobe of each lung is the only part in contact with 

 the basal portion of the heart (Plates VIII and IX). These 

 lobes present a triangular area in contact with the heart 

 which may be bounded below by a line from the lower 

 part of the sixth thoracic vertebra to the middle of the 

 fourth sternochondral articulation on the right side and 

 from the same vertebra to the sixth costochondral articula- 

 tion on the left side. In each case this area touches 

 both auricle and ventricle and on the left side the 

 apex of the heart (Plates VIII to XII). The middle 

 lobe of the right lung comes into contact with the right 

 auricle near its upper and posterior part at the level of the 

 disc between the sixth and seventh thoracic vertebrae and 

 the third costal cartilage. The area covered by this lobe 

 increases from above downward as that covered by the 

 superior lobe decreases. At the level of the fourth car- 



