On Respiration 201 



convulsive movement of the body accompanied by a 

 sudden shout. 



The asthmatic paroxysm which accompanies palpi- 

 tation of the heart will be discussed in the Seventh 

 Chapter of the Treatise On Muscular Motion. 



So much then for inspiration which is effected by 

 the aforesaid muscles. When, however, their con- 

 traction ceases the ribs sink of their own accord to 

 their natural position, and the diaphragm, now relaxed 

 and flaccid, is raised into the cavity of the thorax by 

 the upward pressure of the viscera. And this we 

 have said takes place without any muscular action in 

 the case of a dead animal. And finally, when the 

 chest is narrowed at almost every part, the lungs 

 must be compressed by it and the air expelled ; so 

 that clearly the lungs do not subside of themselves, but 

 follow the movement of the thorax. 



But to more violent expirations the abdominal 

 muscles also contribute. For the obliquely ascending 

 and descending muscles (whose tendons are inserted 

 into the lower ribs), in their contraction, draw the 

 ribs downwards and narrow the chest. Further, the 

 whole abdominal muscles simultaneously contracting, 

 press the viscera which lie under them, so that the 

 diaphragm is driven by their pressure and forcibly 

 urged up into the chest. And any one can find out 

 in his own case that in sneezing, coughing, laughing, 

 and in every violent expiration, the muscles of the 

 abdomen are drawn together and contract. Hence in 

 laughter and in violent expirations the hypochondria 

 often suffer pain from the convulsion of the aforesaid 

 muscles. 



From this we gather that laughter takes place 

 without any action or contraction of the diaphragm. 

 For in laughter the diaphragm is not, as some have 



