RESPIRATION 



197 



expand either upwards, inwards, or backwards. It is 

 probably for this reason that the friction sound of 

 pleurisy is usually best heard over the antero-lateral 

 aspect of the chest wall. The expansion of the apices, 

 on the other hand, is relatively feeble, and can only 



FIG. 12. EIGHT LUNG FROM THE SIDE, SHOWING DIRECTIONS 

 OF EXPANSION. (KEITH.) 



take place indirectly and chiefly through the diaphragm 

 allowing descent of the lung as a whole, and some writers 

 have ascribed to this fact the liability of the apices to 

 become the seat of tuberculous deposits (Figs. 11, 12, 

 and 13). 



In forced inspiration all the muscles which can in any 



