i o THE INVOL UNTAR Y NER VO US S YSTEM 



and excitor elements, with their sensory cells and sensory fibres, 

 their intermediary cells and connector fibres and their motor cells 

 and motor fibres ? This book is an attempt to do so, and to put 

 the involuntary nervous system on the same footing as the volun- 

 tary system. I propose to trace out the history of this involun- 

 tary system and show how our conceptions have been modified 

 from time to time, to give our present knowledge, physiological 

 and anatomical, of the different motor neurons of the system, and 

 to give the evidence upon which it is possible to suggest the 

 reason why the motor neurons of the involuntary tissues of the 

 vertebrate have come to occupy their present position. 



I will begin with the history of the sympathetic nervous 

 system. The striking point about the sympathetic nerve, which 

 distinguished it from all other nerves in the eyes of anatomists 

 in the early days, was the presence of little knots or ganglia 

 along the whole of its course ; and as these could be traced up 

 to the cranial region they concluded that the sympathetic nerve 

 arose from the cranial region in the neighbourhood of the vagus 

 and passed down to the end of the body. 



Against this view of the cranial origin of the sympathetic 

 nerve Petit urged that stimulation of the cervical sympathetic 

 caused dilatation of the pupil, and Winslow pointed out that the 

 branches from the superior cervical ganglion towards the cranial 

 nerves diminished in calibre, a fact which was not in accordance 

 with their origin from the cranial nerves. He considered the 

 ganglia to be scattered centres of origin of the sympathetic 

 system and called them the little brains of that system. 



Haller's discovery of the existence of communications be- 

 tween the ganglia and all the spinal nerves, to which he gave the 

 name " rami communicantes" threw an absolutely new light on 

 the sympathetic system and has been the basis of all subsequent 

 investigations. 



_ 



Of all those in the past whose influence has produced most 

 effect upon our conceptions of the sympathetic system, the name 

 of Bichat comes prominently forward. He taught that two 

 great systems existed in every vertebrate, the one concerned with 

 the outside world, represented by the organs of locomotion and 

 external sense-organs, to which he gave the name animalic ; the 

 other concerned with the regulation of the nutrition of the body, 

 to which he gave the name organic. Each of these systems had 



