1846 HUMAN ANATOMY. 



encroach somewhat anteriorly in the left, terminating belo\^ the lingula. The left 

 lung is thus di\'ided into a superior and an inferior lobe. In the right lung a middle 

 lobe is cut off from the superior by a secondary Jissiwe, which starts from the main 

 iissure far back on the lateral aspect and runs forward, either straight or with an 

 upward or a downward inclination. The foregoing description applies to the course 

 of these fissures as seen on the surface ; but the chief fissure is, moreover, very deep, 

 penetrating to the main bronchus, and completely dividing the lung into a part above 

 it and one below it. The depth from the surface of an inflated lung to the bronchus 

 at the bottom of the fissure ( taken at the point of origin of the secondary fissure on 

 the right and at a corresponding point on the left) is from 7-8 cm. on the right and 

 about I cm. less on the left. The secondary fissure is much less deep and may end 

 prematurely, or even be wanting, so that the middle lobe is a very irregular structure. 

 The left superior lobe qomprises the apex and the entire front of the lung, while 

 the inferior takes in most of the back and all of the base, unless the lingula bt re- 

 garded as constituting its anterior border. In the right lung the middle lobe forms 

 a varying part of the front and one-fourth or one-third of the base. The volume of 

 the upper and lower lobes of the left lung is about equal. In the right lung that of 

 the inferior is about equal to that of the other two. We consider the middle lobe 

 simply as a piece cut off from the upper, so that the right upper and middle lobes 

 correspond to the left upper one. 



Variations of the Lobes and Fissures. — Were it not for the great difficulty in properly 

 examining the lungs, their marked tendency to variation would doubtless be more fully appre- 

 ciated. Schafifner ' has shown that an accessory inferior lobe is very frequently found on the 

 under surface, extending up onto the inner surface in front of the broad ligament. This lobe 

 may be merely indicated by shallow fissures or sharply cut off from the rest. It may present 

 a tongue-like projection inward or may comprise the entire inner portion of the base. It usu- 

 ally represents, when present, from one-fifth to one-third of the base. It may occur on either 

 side or on both, but is larger and more frequently well defined on the right. On the other hand, 

 it is present, or at least indicated, rather more often on the left. Schaffner found it in 47. i per 

 cent, of 210 lungs. The lobe of the right lung represents the subcardiac lobe of many mam- 

 mals, that of the left being evidently its fellow. The irregularity and occasional absence of the 

 fissure marking off the middle lobe have been mentioned. An irregular fissure may subdivide 

 the left lung into three lobes, and both lungs may exceptionally be still further subdivided, espe- 

 cially the right one. A little process of the right lung just above the base, behind the termina- 

 tion of the inferior vena cava, may very rarely become more or less isolated as the lobus cavce. 

 The azygos major vein may be displaced outward, so that, instead of curving over the root 

 of the lung, it may make a deep fissure in the upper part of the right lung, "marking off an 

 extra lobe. 



External Appearance and Physical Characteristics.— The adult lung 

 is bluish gray, more or less motded with black. At birth the lung-tissue proper is 

 nearly white, but the blood gives it a pinkish or even a red color. It grows darker 

 with age, pardy, perhaps chiefly, by the absorption of dirt, but also by the greater 

 quantity of pigment. Before middle age the lungs become decidedly dark by the 

 presence of black substance (be it dirt or pigment), arranged so as to bound 

 irregular polygons from 1-2.5 cm- in diameter, which are the lobules. At first, 

 while the black is scanty, the lines seem to enclose considerably larger spaces, but 

 when more of the lobules appear, owing to a greater deposit of the pigment in the 

 areolar tissue and lymphatics marking them off, it is clear that their diameter rarely 

 much exceeds 1.5 cm. Some, however, are relatively long and narrow. It is re- 

 markable that the deposit of pigment is much greater in certain places than in others. 

 Thus the rounded posterior parts of the lungs are darker than the anterior portions. 

 In general the external surface is much darker than the mediastinal or the base, while 

 the surface within the fissures is the lightest of all. Moreover, the pigment on the 

 external surface, before the coloration has become general, is often in^tripes corre- 

 sponding to the intercostal spaces, as if there were more pigment in the places most 

 accessible to light. 



The lungs being filled with air, after respiration has begun, are soft and crack- 

 ling on pressure. They are extremely elastic, so as to collapse to perhaps a third 

 of their size when the chest is opened. 



1 Virchow's Archiv, Bd. clii., 1898. 



