VOMITING. 305 



longitudinal fibres of the oesophagus, and the abdominal 

 muscles. The muscular coats of the stomach itself are re- 

 laxed, or, at all events, their contraction has no marked in- 

 fluence in the expulsion of its contents. 



The most important muscle concerned in this act is the dia- 

 phragm ; and it has been shown that this muscle alone is capa- 

 ble of producing vomiting when the abdominal muscles have 

 been divided. 1 The action of the diaphragm is to forcibly 

 press the stomach against the anterior wall of the abdomen 

 and the linea alba, at the same time, by its descent, forming 

 a tendency to a vacuum in the chest and dilating the oesoph- 

 agus, as the air cannot enter the lungs, owing to closure 

 of the glottis. The contractions of the longitudinal fibres of 

 the oesophagus are probably important in assisting to relax the 

 cardiac opening of the stomach, counteracting, at the same 

 time, the contractions of the pillars of the diaphragm. The 

 contractions of the abdominal muscles assist in expelling the 

 contents of the stomach, but are much less effectual than the 

 contractions of the diaphragm. It has been shown that they 

 are frequently incapable, in themselves, of producing vomit- 

 ing when the diaphragm has been paralyzed. They always 

 act, however, as can be readily observed by simple external 

 examination. 



The vomited matters pass readily into the mouth, and 

 seldom, if ever, into the glottis, which is firmly closed. The 

 velum is generally contracted and applied to the pharynx so 

 as to protect the nasal passages ; but this is not always effec- 

 tual, for matters sometimes pass into the nose when the act 

 is very sudden or when the mouth is not sufficiently opened. 



After the act has been accomplished by one, or several 

 successive contractions, it is followed immediately by a pro- 

 longed expiration and a sense of relief from the distressing 

 nausea. It is frequently repeated, however, at intervals 



1 In birds, the abdominal muscles perform the most important part in vomit- 

 ing. 



20 



