CONNECTIONS OF THE LUNGS. 



309 



part of the cartilage of the fifth rib. Two fissures are seen in the border 

 of the right lung, but only one in that of the left. The posterior border 

 is as long again as the anterior, and projects inferiorly between the lower 

 ribs and the diaphragm ; it is thick and vertical, and is received into the 

 hollow by the side of the spinal column. 



The outer surface of the lung is convex, and is in contact with the wall 

 of the thorax : a large cleft divides it into two pieces (lobes of the lung), 

 and on the right side there is second smaller fissure. The inner surface is 

 flat when compared with the outer ; altogether in front is the hollow cor- 

 responding with the heart and its large vessels, which is greatest on the 

 left lung ; and behind this, but nearer the posterior than the anterior 

 border, is a fissure about three inches long, hilum pulmonis, which receives 

 the vessels forming the root of the lung. 



Fig. 97. 



DIAGRAM TO SHOW THE DIFFERENCE IN THE ANTERIOR BORDER OF THE RIOHT AND LKFT LTNO, 

 the edge being indicated by the dark line ; and to mark the different level of the base on the 

 two sides. 



Each lung is divided incompletely into two parts or lobes by an oblique 

 fissure, which begins near the apex, and ends in the anterior border near 

 the base : from the form of the lung and the direction of the fissure the 

 lower lobe is necessarily the largest. In the right lung a second horizontal 

 fissure is directed forwards from the middle of the oblique one to the ante- 

 rior border, and cuts off a small triangular piece from the upper lobe : this 

 is the third lobe of the lung. Occasionally there may be a trace of the 

 third lobe in the left lung. 



Besides the difference in the number of the lobes, the right lung is larger 

 and heavier, and is wider and more hollowed out at the base than the left ; 

 it is also shorter by an inch. The increased length and the narrowness of 

 the left lung are due to the absence of a large projecting body like the 

 liver under it, and to the direction of the heart to the left side. 



