l8 UNIVERSITY OF MISSOURI STUDIES 



the lung in the sixth intercostal space, about 1.5 cm. exter- 

 nal to the midclavicular line. The horizontal fissure begins 

 in the great iissure just posterior to the midaxillary line 

 and runs inward and a little downward behind the third in- 

 tercostal space to end in the anterior margin of the lung 

 behind the fourth sternochondral articulation. The great 

 fissure of the left lung begins behind, a little higher than 

 that of the right lung. It is, at iirst, at the level of the disc 

 between the third and fourth vertebrae and runs downward 

 and outward across the fourth intercostal space and the fifth 

 rib to cross the midaxillary line in the fifth intercostal 

 space. Here it takes a more vertical direction and ends in 

 the inferior margin of the lung at the upper border of the 

 sixth rib a little external to the midclavicular line. A very 

 narrow strip of the external part of the inferior lobe is 

 seen, in the anterior view, near the outer part of the base of 

 each lung. The remainder of the lung seen in anterior view 

 is formed by the superior and middle lobes on the right side 

 and the superior lobe on the left side (Plates XXVIII and 

 XXXII). Posteriorly, the upper third is formed by the 

 superior lobe in each case, while the remainder is formed by 

 the inferior lobe. 



The internal surface of each lung, which also extends 

 from apex to base, is shorter and more irregular in contour 

 than the external surface. It is concave in all directions. 

 The concavity is more marked from before backwards than 

 from above downwards, and in the lower two-thirds than 

 in the upper third. That of the left lung is much more 

 marked than the right (Plates X, XI, XII, XXVIII and 

 XXXII). For convenience of description the internal sur- 

 face of each lung may be divided into four areas. The first 

 area may be made to include the hilus, the second, the 

 region above the hilus, corresponding to the superior media- 



