TOPOGRAPHY OF THE THORAX AND ABDOMEN 1 7 



continuous with the inferior margin of the lung in the fifth 

 intercostal space. 



The posterior border (or posterior surface) of each 

 lung is separated from the corresponding internal surface 

 by a ridge — crista pulmonis of Merkel — more plainly seen 

 above the hilus than below it (Plates VI and VII). The 

 crista of the right lung (seen in projection in Plates XXIX 

 and XXXIII) lies anterior to the right half of the vertebral 

 column from the second to the ninth thoracic vertebra. It 

 becomes continuous with the posterior part of the inferior 

 margin opposite the disc between the ninth and tenth ver- 

 tebrae. The crista of the left lung lies a little farther from 

 the midline and extends down to the side of the tenth verte- 

 bra where it turns outward to join the inferior margin in 

 the tenth intercostal space, at the level of the disc between 

 the tenth and eleventh vertebrae. 



The external surface of each lung is convex in all di- 

 rections and presents a regular curve from apex to base 

 which follows the concave internal surfaces of the thoracic 

 wall. These surfaces are crossed by oblique grooves which 

 are the external limits of the fissures dividing the lungs 

 into lobes. The lines in the projections indicating these 

 fissures represent them as seen on the surfaces of the lungs. 

 It must be borne in mind that the relations of a iissure to the 

 ribs when seen from the front or back (Plates XXVIII, 

 XXIX, XXXII and XXXIII) do not correspond exactly to 

 those when seen from the sides, (Plates XXX, XXXI, 

 XXXIV and XXXV). 



The great fissure of the right lung begins behind, oppo- 

 site the centrum of the fourth vertebra, between the spines 

 of the third and fourth vertebrae, passes outward under 

 cover of the fifth rib to cross the midaxillary line in the 

 fifth intercostal space and ends in the inferior margin of 



