CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 403 



two vagi after forming the oesophageal plexus on the oesophagus 

 are gathered together again as two main trunks which run along 

 the oesophagus, the left in the front the right at the back, to the 

 stomach. The left, or anterior nerve is distributed to the smaller 

 curvature and the front surface of the stomach, forming a plexus 

 in which nerve-cells are present ; and branches pass on to the liver 

 and probably to the duodenum. The right, or posterior nerve is 

 distributed to the hinder surface of the stomach, but only to the 

 extent of about one-third of its fibres ; about two- thirds of the 

 fibres pass on to the solar plexus. The fibres of the vagus nerves 

 thus distributed to the stomach are for the most part non- 

 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 coeliac 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 muscularis mucosae ; 

 whether any are connected with the gastric glands, and if so how, 

 is not at present known. 



There are no facts which afford satisfactory evidence that any 

 part of this arrangement of nerves supplies such a local nervous 

 mechanism as was suggested above. The importance however of 

 such a local mechanism whatever its nature, and the subordinate 

 value of any connection between the gastric membrane and the 

 central nervous system, is further shewn by the fact that a secretion 

 of quite normal gastric juice will go on after both vagi, or the 

 nerves from the solar plexus going to the stomach have been divided, 

 and indeed when all the nervous connections of the stomach are as 

 far as possible severed. And all attempts to provoke or modify 

 gastric secretion by the stimulation of the nerves going to the 



262 



