PHYSIOLOGY FOR BEGINNERS 



CHAP. 



upper limit of the cavity. The wall of the thorax is also 

 covered by large muscles passing both from the back and 

 from the front over the sides of the chest to the arms. Over 

 these muscles is a little fat, and then the skin. 



Lining the inner surface of the wall of the thorax is a thin 

 membrane, called the pleura, like the peritoneum lining the 

 inner surface of the wall of the abdomen. The pleura is, 

 however, in two parts, one for each side of the chest, with 

 the heart between the two. 



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FIG. 5. Diagram of a transverse section of the chest showing the heart and lungs 



in place. 



DV, dorsal vertebra ; Ao, aorta ; Ao', part of aorta descending to abdomen ; SC, 

 superior vena cava ; PA, pulmonary artery dividing iijto a branch for each 

 lung; LP y RP, left and right pulmonary veins; Br, bronchi; RL, LL, right 

 and left lungs ; (E, oesophagus ; /, pericardium ; //, the two layers of pleura ; 

 v, a vein. A space, shaded, is represented between the two layers of pleura ; 

 such a space does not in reality exist. 



Situation of the Thoracic Organs. The lungs are 

 situated one in each lateral half of .the chest ; each is quite 

 free and separate from the wall except at one place, where it 

 is fixed to the vertebral column ; this is just where the vessels 

 from the heart and the tube from the trachea go into it. Now 

 the pleura on each side lines the whole wall of the chest, 

 except where each lung is fixed to the vertebral column, for 

 where it meets the root of the lung, as this is called, it passes 



