128 



JIf.UA.V BIOLOGY 



on each side of the spinal column and tied together below ; 

 for both chains of ganglia end in the same ganglion in 

 the pelvis. Some of the fibers from the spinal cord pass 

 through these ganglia on their way to the viscera, losing 

 their white sheaths in the ganglia and emerging as gray 

 fibers. The spinal cord and brain with the fibers which 

 do not pass through the double chain of ganglia are called 



the cere bro - spinal system. 

 The double chain of ganglia 

 and the fibers which go 

 through them are called the 

 ganglionic or sympathetic 

 system. 



Why these Nerves are 

 called the Sympathetic 

 System. — These nerves, 

 after leaving the double 

 chain of ganglia, form many 

 intricate networks of ganglia 

 and fibers. Each network 

 is called a plexus (Fig. 116). 

 The largest of the plexuses 

 is just back of the stomach, 

 and is called the solar plexus. 

 A blow upon the stomach 

 may paralyze this plexus 

 The plexuses and fibers con- 

 nect the viscera so perfectly that one organ cannot suffer 

 without the others changing their activity, or sympathising 

 with it. An overloaded stomach causes the heart to 

 beat faster and send it more blood ; a loss of appetite 

 usually accompanies illness and allows the stomach to 

 rest. This sympathy is necessary, for if one organ is 



Fig. 116. — Diagram of Sympa- 

 thetic System showing double 

 chain of ganglia ; also plexus at 

 heart and solar plexus. 



and cause sudden death. 



