HUMAN ANATOMY. 

 encroach somc,vl,a, anteriorly in the left, temtatinB below Imgula The 



Tand onebelow it. The depth from the surface of an inflated lung to the bronchus 

 t he bottom of the fissure (taken at the point of origin of the secondary hssure on 

 th right and at a corresponding point on the left) is from 7-8 crn^ on the right and 

 "cm less on the eft. The secondary fissure is much less deep and may end 

 premature^', or e"n be wanting, so that the middle lobe is a very irregular structure. 

 The left slpcriorlobe comprises 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 be 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 

 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. Schamier 1 has shown that an accessory inferior lobe is very frequently found I on t 

 under surface extending up onto the inner surface in front of the broad ligament. I his 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 47.1 per 

 cent, of 210 lungs. The lobe of the right lung represents the subcardidC 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 1. it 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 cav&. 

 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 i^iuy, more or less mottled 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 HVM\ partly, 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 f black substance (be it dirt or pigment), arranged so as to bound 

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

 while tin- 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- 

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

 Thus the mumled posterior parts of the lunys are darker than the anterior portions. 

 In general the .-\ternal surface is much darker than the mediastinal or the base, while 

 the sui-iacr within the IISMIH s is the lightest of all. Moreover, the pigment on the 

 external Miitace, 1>< fore the coloration has become general, is often in stripes corre"- 

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



accessible to light. 



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

 ling "ii pressure. The\ are extremely elastic, so as to collapse to perhaps a third 



of their -.\/r \\hen the client is opened. 



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



