CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 427 



medullated fibres ; by the time the vagus reaches the abdomen it 

 consists almost exclusively of non-medullated fibres, medullated 

 fibres being very few; the large number of medullated fibres 

 which the nerve contains in the upper part of the neck pass off 

 into the laryngeal, cardiac and other branches. 



From the solar plexus nerves, arranged largely in plexuses, 

 pass in company with the divisions of the cceliac artery, coronary 

 artery of the stomach and branches of the hepatic artery, to the 

 stomach. Though the two abdominal splanchnic nerves which 

 join the solar plexus (semilunar ganglia) are chiefly composed of 

 medullated fibres, the nerves which pass from the plexus to the 

 stomach are to a large extent composed of non-medullated fibres. 

 All these nerves, both the branches of the vagi and those from the 

 solar plexus, lie at first in company with the arteries on the sur- 

 face of the stomach beneath the peritoneum. From thence they 

 pass inwards, still in company with arteries, and form on the 

 one hand a plexus, containing nerve-cells, between the longitu- 

 dinal and circular muscular coats corresponding to what in the 

 intestine we shall have to speak of as the plexus of Auerbach, 

 whence fibres are distributed to the two muscular coats, and on 

 the other hand a plexus in the submucous coat, also containing 

 nerve-cells, corresponding to what is known in the intestine as 

 Meissner's plexus. From this latter plexus fibres pass to the 

 mucous membrane ; some of these end in the blood vessels or in the 

 muscularis mucosse, others, as we have said, are probably connected 

 with the gastric glands. 



That the secretion of gastric juice (we shall speak of the move- 

 ments of the stomach, and with these of the vascular changes later 

 on) may be influenced by the central nervous system through the 

 one or the other of these two sets of nerves is shewn by many facts. 

 For instance, in cases of gastric fistula, where by complete occlusion 

 of the oesophagus stimulation by the descent of saliva has been 

 avoided, the presence of food in the mouth or the mere sight or 

 smell of food has been seen to provoke a lively secretion of gastric 

 juice. This must have been due to some nervous action ; and the 

 same may be said of the cases where emotions of grief or anger 

 suddenly arrest the secretion going on or prevent the secretion 

 which would otherwise have taken place as the result of the 

 presence of food in the stomach. The secretion excited by the 

 sight or smell of food is said not to take place if both vagus nerves 

 be previously divided; and it has been suggested that while 

 impulses reaching the stomach along these nerves excite secretion, 

 those reaching the stomach along the sympathetic nerves inhibit 

 secretion; but this has not as yet been definitely proved and 

 stimulation of the two sets of nerves has not so far given satis- 

 factory results. 



On the other hand that the connection of the stomach with the 

 central nervous system by means of these nerves is of relatively 



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