256 



THE NERVOUS SYSTEM 



the bladder. The innervation of this viscus is shown in 

 Fig. 37. After section of the nerves going to the inferior 

 mesenteric gangUon, when the left hypogastric nerve is 

 cut and its central end stimulated, the right half of the 

 bladder contracts. This is due, as Langley and Anderson 

 showed, to the division of each axon going to the inferior 



Sp cord 



Inf. meig --f 

 Post -ganglionic fibre 



^ 'Pre -ganglionic fibre 

 -Hypogastric nerves 



Fig. 37. — Diagram to show the axon-reflex in the innervation of the 

 bladder. The axons divide at x (from the Journal of Physiology). 



mesenteric ganglia. Such an effect is termed an Axon- 

 reflex. 



The question now arises, if nerve-fibres can conduct 

 impulses in both directions, do they do so under natural 

 conditions ? It is usual to regard nerve-fibres as either 

 exclusively motor or exclusively sensory, but the anti- 

 dromic impulses (p. 87) seem to indicate that the posterior 

 root-fibres, in addition to conveying sensory impulses 

 centrally, convey vaso-dilator impulses peripherally. Again, 



