On Muscular Motion and Animal Spirits 289 



where shown ; and the diaphragm, in contraction, is 

 brought towards a plane but never recedes from it, 

 as appears from what has been premised. 



I admit that in wounds of the chest or of the 

 diaphragm itself, the diaphragm is sometimes convex 

 downwards, but this does not occur in inspiration nor 

 does it arise from the lungs taking a long breath ; it 

 happens only in the contraction of the chest and in 

 expiration. For, indeed, in the dilation of the chest 

 gaping from a wound it has suffered, the air rushes 

 partly through the trachea into the lungs, but partly 

 also, by reason of its own elastic force, makes its way 

 through the opening of the wound into the cavity of 

 the chest ; so that when in expiration the space of 

 the chest is suddenly diminished, the air contained in 

 the cavity between the lungs and the internal wall of 

 the chest, as it cannot at once escape through the 

 wound, compressed by the contraction of the chest, 

 pushes the diaphragm, which is in diastole and 

 relaxed, and pressing it downwards makes it convex, 

 as I have assured myself by inspection in vivisections. 



It is to be further noted as to the diaphragm that 

 its fleshy fibres proceeding from its membranous 

 centre, go out into the surrounding parts, into which 

 it is inserted : whence it comes about that as some 

 fibres stretched out in one direction, some in the 

 opposite, contract with equal effort, the membrane 

 between them is held in equilibrium : yet meanwhile 

 the diaphragm as a whole is carried downwards and 

 outwards, just as if it had fibres stretched over the 

 whole of its length. 



