THE LUNGS. 1095 



much more sharply marked groove runs upwards, and laterally over the apex 

 pulmonis a short distance, from the summit. This is the sulcus subclavius, and it 

 contains the left subclavian artery when the lung is in place. Ventral to the 

 subclavian sulcus a shallow wide groove, also leading to the ventral aspect of the 

 apex, corresponds to the left innominate vein. In the right lung the hilum is also 

 circumscribed above by a curved groove, which is narrow and more distinctly 

 curved than the aortic groove on the left side. It lodges the vena azygos as it 

 turns ventrally to join the vena cava superior. From the ventral end of the 

 azygos sulcus a wide shallow groove extends upward to the inferior part of the 

 anterior aspect of the apex pulmonis. This is produced by the apposition of the 

 lung with the vena cava superior and the right innominate vein. Close to the 

 summit of the apex there is also, on its medial aspect, a sulcus for the superior 

 end of the innominate artery. 



In addition to the hilum, it must now be evident that the mediastinal surface of 

 each lung presents three areas which correspond respectively with (1) the middle 

 mediastinum (i.e. the pericardial hollow), (2) the dorsal mediastinum, and (3) the 

 superior mediastinum ; and that in each of these districts impressions corresponding 

 to structures contained within these portions of the interpleural space may be 

 noticed. 



The dorsal part of the lung at the junction of the costal and mediastinal 

 surfaces is thick, long, and rounded. It forms the most bulky part of the organ, 

 and occupies the deep hollow in the thoracic cavity which is placed at the side 

 of the vertebral column. 



The ventral border or margo anterior of the lung is short, and exceedingly 



thin and sharp. It begins abruptly immediately below the groove on the apex 



for the innominate vein, and extends to the base, where it becomes continuous 



i with the sharp inferior border. The thin ventral part of the lung is carried 



ventrally and medially, ventral to the pericardium, into the narrow pleural costo- 



1 mediastinal sinus, dorsal to the sternum and costal cartilages. The ventral border 



of the right lung fills up this recess completely, and in the upper par't of the 

 i chest is separated from the corresponding border of the left lung only by the two 

 i layers of mediastinal pleura which are reflected from the sternum to the pericardium. 



The ventral border of the left lung, in its lower part, shows a marked deficiency 

 or notch, the incisura cardiaca, corresponding to the apex of the heart, and where 

 this exists the lung margin leaves a considerable portion of the pericardium un- 

 covered, and fails to fill up completely the costo-mediastinal sinus of the pleural 

 cavity. During respiration the ventral margin of the left lung at the incisura 

 cardiaca advances and retreats to a small extent in this pleural sinus, ventral to 

 the pericardium. 



Fissures and Lobes of the Lung. The left lung is divided into two lobes 



by a long deep fissure, the incisura interlobaris, which penetrates its substance to 

 within a short distance of the hilum. On the upper and lower sides of the hilum 

 this fissure cuts right through the lung and appears on the mediastinal surface. 



| Viewed from the costal surface, it begins dorsally about two and a half inches 

 below the apex, about the level of the vertebral end of the third rib, and is 

 continued downwards and ventrally in a somewhat spiral direction to the 

 diaphragmatic surface of the lung, which it reaches a short distance from its 

 ventral end. The lobus superior lies above and ventral to this cleft. It is 

 conical in form, with an oblique base, and the apex and the whole of the ventral 

 border of the lung belong to it. The lobus inferior lies below and dorsal to the 

 fissure. It is the more bulky of the two, and includes almost the entire dia- 

 phragmatic surface and the greater part of the thick dorsal part of the lung. 



In the right lung there are two incisurse interlobares, which subdivide it into 

 three lobes. One of the incisurse interlobares is very similar in its position and 

 relations to the fissure in the left lung. It is directed, however, rather more 

 vertically, and ends somewhat farther from the median plane. It separates the 

 lobus inferior from the lobus medius and lobus superior. The second incisura 

 interlobaris begins in the main fissure at the dorsal part of the lung, and proceeds 

 Centrally, to end at the ventral border of the lung at the level of the fourth costal 



70 I 



