922 



THE ORGANS OF RESPIRATION 



cially the case in the regions of tlie intVi-ior, and the lower i)arts of the anterior 

 borders where two layers of parietal pleura are in contact with each other, these 

 regions are known asthe pleural sinuses, and tliey vary in extent with the disten- 

 sion of the lungs. 



The right pleural sac, though shorter and wider than the left, reaches as a rule 

 somewhat higlier in the neck. 



The Lungs. — Each lung presents an outer and an inner surface, se})arated by 

 an anterior and a posterior l)order, with a base and an apex. 



The outer surface is convex, and mainly corresiwnds to the concavity of tlic 

 iimer surface of Xho lateral wall of the thorax. 



The inner surface is concave, and comes into contact Avith the pericardium and 

 lateral pleural wall of the mediastinal spaces. 



Fio. .^43. — Anterior View of the Thorax with Chest Wall removed, showing the 

 Lungs. (Modilied from Bourgery. ) 



Peetoralis major muscle 

 Pectoralis minor muscle 



SUPERIOR LOBE 



Serratus magnus 

 muscle 



INFERIOR LOBE 



Diaphragm 



STERNUM 



INFERIOR LOBE 



SECTION OF SEVENTH RIB 



ENSIFORM CARTILAGE 



The posterior border is the longer; it is thiek, rounded, and siimotli, and 

 occupies the groove on tlie side of the vertebral eolumn. 



The anterior border is thin, irregular, and sharply edged, and is deeply notehed 

 in the left lung leaving the pericardium uncovered. 



The base is concave, and rests on the corresponding arch of the diaphragm ; 

 whilst the apex passes above the anterior part of the first rib to lie beneath the 

 subclavian artery. Each lung is divided into two lobes by a deep fissure which 

 passes obliiiuely upwards and inwards almost to the root of the organ. This fissure 

 commences at the posterior l)order, about 7 '5 cm. below the a])ex, and, sweeping 

 round the convex surface of the lung, ends near the anterior boixler below. 



In the right lung a second fissure passes from the anterior edge to reach the 

 main fissure near its centre, marking off a third or middle lobe. 



