210 



VISCERA OF THE CHEST. 



Owing to the division of the muscles, the pharynx has 

 fallen down and concealed the larynx. 



FIG 20. 



A TRANSVERSE SECTION OF THE THORAX, SHOWING THE THREE 

 SEROUS SACS WITHIN THE CAVITY. 



The dark substance surrounding the outside indicates the flesh, and the ichlte body at the top 



is the Tcrtebrce. 



B, B, The ribs. P, The pericardium. 



E, The sternum, and the cartilages of F, The fibrous layer of the pericardium. 



the ribs. By tracing the finer white line the reader 



PC, The pleura costalis. will discover there are three sacs in 



PL, The pleura pulmonaris. this figure. A mediastinum is formed 



L, L, The lungs. in the centre, where they meet. 



H, The heart. 



VISCERA OF THE CHEST. 



The pleurcB (Fi rj 20 . PL . PC).— When the chest is 

 opened, a smooth polished membrane is seen, covering its 

 internal surface, and investing its contents. Each side of 

 the chest has its particular pleura, or serous membrane, 

 which is distinct from that of the other. There is, besides, 

 a third serous membrane within the chest, which covers 

 the heart, and lines the pericardium or heart bag (Fig 20 . 



