THE MOVEMENTS OF THE STOMACH 747 



contraction of the diaphragm and of the abdominal muscles. At the same 

 time the cardiac orifice is relaxed. By means of X-rays it may be seen that 

 at this time a strong contraction occurs at the incisura angularis, dividing 

 the stomach into two separate portions. The dilated body of the stomach 

 is pressed between the abdominal muscles and the diaphragm, so that its 

 contents are expelled through the relaxed oesophagus and out through the 

 mouth. As vomiting proceeds the stomach contracts down on the remaining 

 contents, but the main factor in the expulsion is the contraction of the 

 abdominal muscles and diaphragm. In fact, vomiting may be excited in an 

 animal in which the stomach has been replaced by a bladder. 



NERVOUS MECHANISM OF VOMITING 



Normally the action of vomiting is reflex. It can be excited by tickling 

 the back of the throat, when the afferent nerves are the trigeninal and the 

 glossopharyngeal, or by irritation of the stomach through the afferent fibres 

 of the vagus. But it may be excited from almost any of the abdominal 

 viscera, e. g. uterus, kidney, intestines, etc. It may also be excited reflexly 

 through the labyrinth or through the eyes, as in vomiting of sea-sickness, 

 and is a marked symptom in many cases of disease of the cerebrum and 

 cerebellum. The efferent impulses are carried by the vagi to the stomach, 

 by the phrenics to the diaphragm, and by the various spinal nerves to the 

 abdominal muscles. There are also inhibitory impulses descending the vagi 

 to the oesophagus and cardiac sphincter. The reflex act depends on the 

 integrity of the medulla, so that a ' vomiting centre ' is sometimes said to 

 be situated in the medulla. 



Drugs may produce vomiting either by irritating the stomach, e.g. 

 mustard and water, zinc sulphate, ipecacuanha, or by direct action on the 

 medullary centres, e. g. tartar emetic, apomorphine, etc. 



