234 RESPIRATION. 



occurs the difference in the two actions. Instead of the 

 vocal cords yielding to the action of the abdominal mus- 

 cles, they remain tightly closed. Thus the diaphragm 

 being unable to go up, forms an unyielding surface against 

 which the stomach can be pressed. It is fixed, to use a 

 technical phrase. At the same time the cardiac sphincter 

 being relaxed while the pylorus is closed (see fig. 65), and 

 the stomach itself also contracting, the action of the abdo- 

 minal muscles, by these means assisted, expels the contents 

 of the organ through the oesophagus, pharynx, and mouth. 

 The reversed peristaltic action of the oesophagus probably 

 increases the effect. 



In the act of voluntary expulsion of urine or fseces, 

 there is first an inspiration, as in coughing, sneezing, and 

 vomiting ; the glottis is then closed, and the diaphragm fixed 

 as in vomiting. Now, however, both the rima glottidis and 

 the cardiac opening of the stomach remain closed, and the 

 sphincter of the bladder or rectum, or of both, being re- 

 laxed, the evacuation of the contents of these viscera takes 

 place accordingly ; the effect being, of course, increased by 

 the muscular and elastic contraction of their own walls. 

 As before, there is as much tendency to the escape of 

 the contents of the lungs or stomach as of the rectum 

 or bladder ; but the pressure is relieved only at the 

 orifice, the sphincter of which instinctively or involuntarily 

 yields. 



In all these expulsive actions the diaphragm is quite 

 passive ; and when it is fixed, it is in consequence of 

 the closure of the glottis (which by preventing the exit of 

 air from the lungs prevents its upward movement), not from 

 any exertion on its own part. 



In females, during parturition, almost an exactly similar 

 action occurs, so far as the diaphragm and abdominal 

 walls are concerned, to that which takes place in a strain- 

 ing effort at expulsion of urine or faeces. The contraction 

 of the uterus, however, is both relatively and absolutely 



