THE MECHANICS OF BREATHING 



287 



diameter of the lower thorax, and, with the diaphragm moving down- 

 wards, the vertical diameter of the whole cavity. 



Inspiration is therefore a very complex act, and it is~owing to the 

 complicated nature of the movements concerned that the lungs are 

 divided into lobes. The upper ribs are chiefly concerned in the 



Lower Bore/, (ex p. 

 Louver Bond, (inspir.) 

 Crus (inspir.) 



Crus (expir.) 



Fto. 163. MEDIASTINAL ASPECT OF RIGHT LUNG TO SHOW RESPIRATORY MOVEMENT 

 OF THE ROOT. (Keith.) 



The cms of the diaphragm is also indicated, and its attachment to the root of the 

 lung through the pericardium. Arrows indicate direction of inspiratory move- 

 ment of various parts of the lung. 



expansion of the upper lobes, the lower ribs in the expansion of the 

 lower lobes, the diaphragm promoting the expansion of the whole 

 lung. 



In the act of inspiration it is also to be noted that, owing to the 

 varying degree of extensibility of the different structures of the lung, 

 the organ expands more in the manner of a Japanes3 fan least in the 

 neighbourhood of the great vessels and bronchi (the root of the lung), 

 most in the outermost zone just beneath the pleura (subpleural zone). 



