308 S. W. RANSON 
rami communicantes from the thoracic and upper lumbar spinal 
nerves; 3) sacral—via the visceral rami of the II, III, and IV 
sacral nerves. The fibers of the thoracicolumbar stream run 
to the sympathetic trunk and are distributed through it to ganglia 
at higher and lower levels. The fibers of the cranial and sacral 
streams make no connection with the sympathetic trunk, but 
run directly to the various plexuses. While the fibers of the 
thoracicolumbar stream end in the ganglia of the trunk or in 
collateral ganglia, those of the cranial and sacral streams end in 
terminal ganglia. In these two respects the cranial and sacral 
streams agree with each other and differ from the thoracicolum- 
bar stream. Also physiologically and pharmacologically the 
two former agree with each other and differ from the latter. It 
is therefore desirable to divide the autonomic nervous system 
into two divisions: 
1. The thoracicolumbar autonomic system (called by many 
physiologists the sympathetic nervous system). 
2. The craniosacral autonomic system (called by many physi- 
ologists the parasympathetic system). 
The importance of this division is further emphasized by the 
fact that most of the structures innervated by the autonomic 
system receive a double nerve supply, being furnished with 
fibers from both divisions of that system. The thoracicolumbar * 
fibers are accompanied in most peripheral plexuses by cranio- 
sacral fibers of opposite function, so that an analysis of these 
plexuses is greatly facilitated by subdividing the autonomic 
system in this way. These statements may be summarized in 
the form of three definitions: 
The autonomic nervous system is that functional division of 
the nervous system which supplies the glands, the heart, and all 
smooth muscle, with their efferent innervation and includes all 
general visceral efferent neurones both pre- and postganglionic. 
The thoracicolumbar autonomic system is that division of the 
autonomic system, the preganglionic fibers of which make their 
exit from the spinal cord through the thoracic and upper lumbar 
spinal nerves. 
