MOTOR FUNCTIONS OF THE BULBO-SACRAL UTFLO W 5 r 



on stimulation of the splanchnic nerve. I have already discussed 

 the share taken by the sympathetic system in the innervation of 

 the small intestine but have not considered the stomach and 

 oesophagus. As far as concerns the oesophagus and its termina- 

 tion in the cardiac sphincter <5f the stomach, there is no evidence 

 that sympathetic motor fibres reach to this region ; the motor 

 supply is entirely from motor cells connected with the vagus 

 nerve. The passage of food from the stomach to the intestine is 

 regulated by a sphincter muscle at the pylorus, and there is some 

 evidence to show that a musculature exists here which is inner- 

 vated after the same fashion as the rest of the sphincter group of 

 muscles already considered. Elliott has given evidence of some 

 contraction of this sphincter muscle in the rabbit upon stimula- 

 tion of the splanchnic nerve, and he finds in the bird a contraction of 

 the whole of the duodenal region upon stimulation of the same 

 nerve. Still more extensive is this musculature in the frog, ac- 

 cording to the evidence of Dixon, who states that the muscula- 

 ture of the whole stomach of that animal contracts either upon 

 stimulation of the splanchnic or in consequence of the direct 

 action of adrenalin. There are then indications in this region of 

 a musculature supplied with sympathetic motor fibres which 

 varies in its extent in different animals, just as according to 

 Elliott (see p. 57) the corresponding sphincter musculature of 

 the bladder varies greatly. Undoubtedly, as in the small in- 

 testine, the musculature of the main body of the stomach in all 

 mammalia is supplied with motor fibres from cells connected 

 with the vagus nerve. 



Where then are the motor cells to this intestinal unstriped 

 musculature, to which the vagus fibres are the connector nerves ? 

 In such a very low vertebrate as the lamprey the fibres of the 

 vagus nerve can be traced in the walls of the intestine and, 

 scattered along the nerve fibres, nerve cells can be seen with 

 which they are in connexion. These scattered nerve cells in- 

 clude among them the motor cells to the intestinal muscle and 

 are situated in the walls of the intestine itself. In the higher 

 forms of vertebrates these nerve cells form a characteristic layer 

 between the circular and longitudinal muscles of the intestine 

 and, with the nerve fibres in connexion with them, are known by 

 the name of Auerbach's plexus. The cells of Auerbach's plexus 

 must in my opinion be regarded as the motor nerve cells, from 



4* 



