56 THE INVOL UNTAR Y NER VO US S YSTEM 



only a few being left intact. The few normal fibres still left in 

 the sacral colonic nerves must belong to the hypogastric nerve, 

 a part of which also runs through the pelvic plexus, either being 

 sensory fibres or possibly connector fibres to motor nerve cells 

 belonging to some part of the internal sphincter of the anus. 

 In another experiment, where both anterior and posterior 

 roots of the cauda equina were cut between the posterior root 

 ganglia and the cord, and time allowed for degeneration, so that 

 the efferent fibres alone would degenerate, these sacral colonic 

 nerves were found to possess a large amount of intact fibres. 

 Langley and Anderson therefore come to the conclusion that the 

 medullated fibres in these nerves are largely sensory, and that the 

 motor cells for the large intestine are mainly situated in the part 

 of the pelvic plexus which lies directly on the rectum and gives 

 origin to the sacral colonic nerves. Similarly, the anterior branch 

 of the pelvic nerve connects with the vesical plexus, in which lie 

 the motor cells of the muscles of the bladder. 



I conclude therefore that, for the main mass of bladder muscula- 

 ture and the musculature of the large intestine, the motor cells 

 are situated, not in large isolated ganglia, but in a plexiform 

 arrangement directly upon the surface of the musculature itself; 

 an arrangement of the same kind as is found in the small 

 intestine, where there exists a plexus with nerve cells, known 

 by the name of Auerbach's plexus, the cells of which form the 

 motor cells of that part of the gut, and are connected with the 

 connector fibres of the vagus nerve (Fig. 5.) 



Further, if this pelvic plexus is the homologue of Auerbach's 

 plexus, then instead of being between the circular and longi- 

 tudinal layers it has come out upon the surface of the cloacal 

 part of the gut, just as Auerbach's plexus lies on the surface of 

 the unstriped muscle of the oesophagus at the other extremity of 

 the gut, instead of between the circular and longitudinal muscular 

 layers. 



The comparative anatomy of the hinder part of the gut points 

 to the coprodceum and urodceum as forming originally a continu- 

 ous tube (Fig. 7). Consequently we should expect a similar 

 innervation of the muscular layers of the two parts. In all pro- 

 bability some of the efferent fibres in the sacral colonic nerves 

 are connector fibres to nerve cells situated more peripherally in 

 the walls of the large intestine, and such cells would, if this is the 



