7 2 THE INVOL UNTAR Y NER VO US S YSTEM 



these muscles are situated in the inferior mesenteric ganglia, 

 except a few outlying cells for the internal sphincter ani (Fig. 7). 

 According to Elliott, stimulation of the pelvic nerve causes in 

 the rabbit relaxation of the urethral muscles and sphincter of the 

 bladder and also of the internal sphincter ani. The inhibitory 

 cells for these muscles have therefore travelled out in the sacral 

 outflow, while their motor cells belong to the thoracico-lumbar 

 outflow. On the other hand, stimulation of the lumbar splanchnics 

 or of the hypogastric nerves or the application of adrenalin causes 

 inhibition of the endodermal musculature both in the bladder and 

 the large intestine, the nerve cells, from which these inhibitory 

 nerves arise, being situated in the inferior mesenteric ganglion. 



We see then that the motor cells of the sphincter (sympathetic) 

 muscles of the vesical and intestinal portions of the cloaca have 

 travelled out with the inhibitory cells of its endodermal vesical and 

 intestinal muscles, and are found together in the same ganglion. 



Conversely, the motor cells of the cloacal endodermal muscles 

 are found in the vesical and rectal plexuses and, as already men- 

 tioned, inhibition of the sphincter muscles of this region is 

 brought about by stimulation of the pelvic nerve, the connector 

 fibres of which connect with cells in the same plexuses. Thus 

 the motor cells of the cloacal endodermal muscles have travelled 

 out with the inhibitory cells of the sphincter (sympathetic) 

 muscles of the vesical and intestinal portion of the cloaca, and 

 are found together in the same ganglionic plexus. 



Passing now to the region of the small intestine we find, as 

 might be expected, the same kind of phenomena as in the 

 large, substituting only superior mesenteric ganglion for inferior 

 mesenteric ganglion, and the vagus nerve for the pelvic nerve. 

 Thus the thoracic splanchnics inhibit the endodermal muscula- 

 ture of the small intestine and cause contraction of the sphincter 

 (sympathetic) musculature, namely, the ileo-colic and possibly 

 the pyloric sphincters, the nerve cells in both cases being situated 

 in the superior mesenteric ganglion. The motor cells of the 

 sphincter (sympathetic) muscles of the small intestine have there- 

 fore travelled out with the inhibitory cells of its endodermal 

 musculature, and are found with them in the same ganglion the 

 superior mesenteric ganglion. 



Conversely, the motor cells of the endodermal musculature 

 are found in Auerbach's plexus, and stimulation of the vagus 



