VOMITING PARTURITION. 183 



the blast of air, on escaping from the lungs, is directed by an 

 instinctive contraction of the pillars of the fauces and descent 

 of the soft palate, chiefly through the nose, and any offending 

 matter is thence expelled. 



In the act of vomiting, as in coughing, there is first an in- 

 spiration ; the glottis is then closed, and immediately after- 

 wards the abdominal muscles strongly act ; but here occurs 

 the difference in the two actions. Instead of the vocal cords 

 yielding to the action of the abdominal muscles, 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 abdominal muscles, by these means assisted, 

 expels the contents of the organ through the oesophagus, phar- 

 ynx, and mouth. The reversed peristaltic action of the 

 oesophagus probably increases the effect. 



In the act of voluntary expulsion of urine or faeces, there 

 is first an inspiration, as in coughing, sneezing, and vomiting; 

 the glottis is then closed, and the diaphragm fixed as in vom- 

 iting. 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 relaxed, the evacu- 

 ation 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 re- 

 lieved only at the orifice, the sphincter of which instinctively 

 or involuntarily yields. 



In all these expulsive actions the diaphragm is quite pas- 

 sive ; 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 straining effort 

 at expulsion of urine or faeces. The contraction of the uterus, 

 however, is both relatively and absolutely more powerful than 

 that of the bladder or rectum, although it is greatly assisted 

 by the inspiratory effort, by the fixing of the diaphragm, and 

 by the action of the abdominal muscles, as in the other acts 

 just described. In parturition, as in vomiting, the action of 

 the abdominal muscles is, to a great extent, involuntary more 



