HISTORY OF THE INVOLUNTARY NERVOUS SYSTEM 23 



arranged motor neurons of that musculature, and the fibres in 

 each anterior root make connexion with the motor neurons of 

 many segments (Fig. 2, B). 



Everything therefore points to the conclusion that the so- 

 called sympathetic nervous system consists simply of masses of 

 motor neurons to a special system of muscles, which have left 

 the central nervous system, but are still connected with it by 

 connector fibres in the rami communicantes. By the term motor, I 

 include true motor nerves, nerves inhibitory to muscular move- 

 ments, and glandular nerves. The connector fibres are confined to 

 a limited portion of the spinal cord and constitute the thoracico- 

 lumbar outflow. There are in fact two sets of connector fibres, 

 the one belonging to the voluntary system, which remains in the 

 central nervous system, and the other belonging to the involuntary 

 system, which passes out from the central nervous system in the 

 rami communicantes, to connect with the motor neurons of the 

 involuntary system. 



The study of the evolution of the animal kingdom, as I have 

 pointed out in the " Origin of Vertebrates," brings out promin- 

 ently the enormous importance of the development of the central 

 nervous system in the upward progress of the race : in the struggle 

 for existence, such progress must necessarily be associated with 

 the greater development of the voluntary part of the nervous sys- 

 tem. The whole history of the progressive evolution of the verte- 

 brate animal up to its culmination in man is evidence of the steady 

 growth in bulk and complexity of that part of the central nervous 

 system which is associated with voluntary movements ; it is the 

 growth of will power, with all that that implies, which has led to 

 the domination of man over the rest of the animal kingdom. 

 Such growth of the voluntary nervous system necessitates increase 

 in bulk and concentration ; and so has brought about the large 

 size of the brain. Such being the lines on which evolution has 

 proceeded, it stands to reason that the more this concentrated 

 voluntary system is freed from the subordinate involuntary sys- 

 tem consistently with the continuance of the harmonious inter- 

 action between the two systems, the greater will be the advantage 

 to the animal. This is what embryology teaches : the motor cells 

 of the involuntary nervous system originally formed part of the 

 central nervous system, and by their migration towards the peri- 

 pheral organs freed the central nervous system from a very large 



