THORACIC CAVITY 



ribs, and just below the middle of the twelfth it becomes 

 continuous with the posterior margin, which ascends along the 

 line of the angles of the ribs to the apex. On the left side, 

 at the level of the fourth costal cartilage, the anterior margin 

 of the left pleura turns away from the median plane, for a 

 variable distance, passing behind the fifth costal cartilage at 



Cervical dome of pleura 

 Left subclavian artery 



Left innominate vein 



Left common carotid arter 



Internal mam- 

 mary artery 



Anterior margin 



of right 



pleural sac 



Intercostal nerve 



Pericardium 



M. transversus 

 thoracis 



Diaphragm 



FIG. 8. Diagram to show the parts which lie anterior to the pericardium 

 and heart. The outline of the heart is indicated in red by a dotted line, 

 and the anterior margins of the pleural sacs are represented by blue lines. 



the margin of the sternum, or even 25 mm. (one inch) more 

 laterally; it then descends to the lower border of the sixth 

 cartilage, where it becomes continuous with the lower margin 

 of the pleura, which passes laterally and backwards along the 

 lower border of the sixth cartilage, across the medial end of 

 the sixth space, and across the seventh cartilage to the 

 junction of the cartilage and bone of the eighth rib. The 



