530 THE MECHANICAL PROCESSES OF DIGESTION [CH. XXXV. 



plexuses of nerves and ganglia contained in its walls. The stomach 

 is also connected with the higher nerve-centres by means of 

 branches of the vagi and of the splanchnic nerves through the solar 

 plexus. 



The vagi (especially the left) contain the acclerator nerves of the 

 stomach ; when they are stimulated the result is peristaltic move- 

 ment. The sympathetic fibres are inhibitory ; when they are stimu- 

 lated peristalsis ceases. The cell stations on the course of the vagus 

 fibres are in the ganglion trunci vagi ; the post-ganglionic fibres that 

 issue from this ganglion are non-medullated. 



The sympathetic fibres leave the spinal cord by the anterior roots 

 of the spinal nerves from the fifth to the eighth thoracic. They pass 

 into the sympathetic system, have cell stations in the coeliac ganglion, 

 and ultimately pass to the stomach by the splanchnic nerves. 



It seems probable that automatic rhythmical contraction is inherent 

 in the muscular coat of the stomach, and that the central nervous 

 system is only employed to regulate it by impulses passing down by 

 the vagi or splanchnic nerves. 



The secretory nerves of the gastric glands are treated on p. 485. 



VOMITING. 



The expulsion of the contents of the stomach in vomiting, like 

 that of mucus or other matter from the lungs in coughing, is preceded 

 by an inspiration ; 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. At the same 

 time the cardiac sphincter being relaxed, and the orifice which it 

 naturally guards being dilated, while the pylorus is closed, and the 

 stomach itself also contracting, the action of the abdominal muscles 

 expels the contents of the organ through the oesophagus, pharynx, 

 and mouth. The reversed peristaltic action of the oesophagus 

 possibly increases the effect. 



It has been frequently stated that the stomach itself is quite 

 passive during vomiting, and that the expulsion of its contents is 

 effected solely by the pressure exerted upon it when the capacity of 

 the abdomen is diminished by the contraction of the diaphragm, and 

 subsequently of the abdominal muscles. The experiments and 

 observations, however, which are supposed to confirm this statement, 

 only show that the contraction of the abdominal muscles alone is 

 sufficient to expel matters from an unresisting bag through the 

 oesophagus ; and that, under very abnormal circumstances, the stomach, 



