Integrative Systems 187 



glions with those nearer the neural tube mark the pathways which 

 the migrating cells followed. 



Divisions of Autonomic System 



Inspection of the relations of the autonomic structures discloses 

 some features which are correlated with the general functional charac- 

 teristics of the system. On structural grounds, four regions may be 

 distinguished, briefly defined as follows: 



Cranial (cephalic): connectors from cranial nerves; exciters in 

 terminal ganglions. 



Cervical: no connectors from cervical spinal nerves; exciters in 

 lateral ganglions. 



Thoracolumbar: connectors from nearly all of the thoracolumbar 

 spinal nerves; exciters usually in lateral or collateral ganglions (the 

 exception being those related to the hypogastric nerves). 



Sacral: connectors from sacral spinal nerves pass to exciters in 

 terminal gangliated plexuses. 



On functional grounds, the cervical region disappears. Its connectors 

 all come forward from the trunk. It merely provides exciters to forward 

 impulses received from more posterior segments and therefore is 

 functionally an extension of the thoracolumbar region. Further, the 

 cranial and sacral regions are structurally alike in that their relatively 

 long connectors pass to terminal ganglions, whereas most of the tho- 

 racolumbar connectors are relatively short and pass to exciters in 

 lateral or collateral ganglions. Therefore the four regions reduce to 

 two structural types, the craniosacral and the thoracolumbar. The 

 name "sympathetic,'" originally applied to the whole system, has 

 been replaced by "•autonomic" ("sympathy" being neither anatomic 

 nor physiologic), but it persists (quite illogically) in a narrower sense 

 as applied to the thoracolumbar autonomic division. The cranio- 

 sacral division then becomes the "parasympathetic." 



Autonomic Functions 



Between the craniosacral and thoracolumbar divisions, there are 

 some radical functional differences. The outstanding difference is 

 commonly described by saying that the two divisions are usually 

 "antagonistic" in their mode of action. A difference of this sort is 

 highly significant in view of the fact that many visceral structures 

 receive innervation from both divisions. Perhaps "antagonistic" is not 

 the best word. In so far as it may seem to imply conflict or inhar- 

 monious organization, it is misleading. A device commonly used to 

 hold some mechanical part firmly in place consists in arranging two 



