THE AUTONOMIC NERVOUS SYSTEM 



115 



while we shall find that there are many correspondences 

 between the states of consciousness and the reactions 

 brought about through the autonomic system. 



It will not be profitable to say much about the anatomy 

 of this division of the nervous system. The details are 

 exceptionally difficult. One point, however, must not be 

 omitted: so far as we know, each path from the cord 

 or the brain to any outlying locality reached by autonomic 

 influences is a tandem arrangement of two orders of 

 neurons (see page 33). The neurons of the first order- 



Fig. 21. To contrast the path to the skeletal muscles, already 

 familiar, in which one neuron extends from the central nervous 

 system to the contractile structures with the autonomic path in 

 which two orders of neurons are employed to span the same interval. 

 Cells of visceral muscle are represented at the end of the post- 

 ganglionic fiber. In the interest of simplicity the preganglionic neu- 

 ron is made to influence only one of the lower order. It would really 

 affect several. 



preganglionic, as they are called have their perikarya 

 within the brain or the cord and extend outside to a 

 greater or less distance. They end by forming synaptic 

 connections with neurons of the second order post- 

 ganglionic and these complete the transmission to the 

 secreting or contractile tissues to be affected. The syn- 

 apses between neurons of the first and those of the second 

 order are usually to be found in ganglia, detached collec- 

 tions of 'gray matter variously situated. Two chains 

 of these ganglia are seen in the back of the body cavity, 

 one on either side of the spinal column. Preganglionic 



