xvi THE NERVOUS SYSTEM 235 



these there is another group of nerves and nerve centers 

 known as the sympathetic system. It consists of a chain 

 of ganglia forty-nine in all located on either side of 

 the spinal cord, extending from the base of the brain to 

 the coccyx. It has also four great ganglia, situated 

 a little in front of the chain, together with numerous 

 smaller ganglia located in the visceral organs. Many 

 nerves connect all these ganglia with each other, with 

 the spinal cord and brain, and with the organs of the 

 chest and abdomen. The largest of the four ganglia is 

 called the solar plexus. It is located behind the stomach 

 and in front of the aorta, and sends branches to all the 

 organs of the abdomen, as the stomach, liver, spleen, 

 pancreas, kidneys, and intestines. These ganglia all 

 give off nerves that supply the visceral organs, glands, 

 and the walls of the arteries and capillaries. 



These ganglia and nerves help to regulate the size of 

 the blood vessels, control the action of the involuntary 

 muscles of all the visceral organs, as lungs, heart, 

 stomach, and intestines, and regulate the activity of the 

 secreting glands. They seem to exercise an important 

 control over the vital processes that are carried on 

 unconsciously. 



Most of the internal organs have nerves from the 

 sympathetic system and from the cerebro-spinal system, 

 as the other is called. The two systems form one com- 

 plete, unified nervous apparatus. 



162. Mind and Brain. We know that the mind and 

 the brain are very closely connected, but just what 

 their relation to each other is no one can tell. When 



