130 THE ENGINES OF THE HUMAN BODY 



remarkable kind. The human machine, then, is provided 

 with bellows of a new variety — a pistoned bellows. 



When studying the respiratory chamber and the 

 mechanism of the internal-combustion engine, we found 

 it convenient to lay the cylinder open. We can throw 

 the respiratory chamber of the human machine open in 

 a similar way. This has been done in fig. 32 ; the front 



Rt. Lung ,^ 



Diaphragm.^ 



Windpipe 



— Bronchus 



Hearf- 



chamber 



"Diaphragm 



.-Sfomach 



Fig. 32. — A vertical section of the human thorax exposed by removing 

 the front wall. 



wall has been removed, and the floor and side walls arc 

 seen in section. The shoulders quite mask the true shape 

 of the thorax ; when they are cut away we see that our 

 chests are shaped like a cone, with its apex at the root of 

 the neck and its broad base just above the waist. The 

 upper part of the thoracic cone is filled by the two lungs, 

 with the heart — the great pump — nestling between them, 

 almost hidden by them. The lower part of the thoracic 



