CHAPTER XIX 



THE NERVOUS SYSTEM 



In Chapter III it was stated that eight systems of organs were 

 found in the human body. Six of these systems have been studied, 

 leaving the seventh, i.e. the nervous system, to form the subject 

 matter of this chapter. 



Parts of the nervous system. — The nervous system consists of : 

 (1) the brain and spinal cord, which are contained within the 

 cavities of the ?kull and spinal column ; (2) masses of nerve cell- 

 bodies called s^Tapathetic ganglia, which are situated in the head 

 and neck, also in the thoracic and abdominal cavities ; (3) nerve 

 trunks, which connect the brain, spinal cord, and s;vTnpathetic gang- 

 lia with each other, with the viscera, and with the periphery of 

 the body. All of these structures are made up of nerve tissue. 

 In addition the endings of the nerves distributed to the organs 

 of the special senses, such as the eye, ear, and skin, are in close 

 contact with modified epithelial cells sometimes called organules. 



Functions of the nervous system. — The human nervous system 

 makes possible all the higher functions of human life. It enables 

 us to think and to will, to recognize our surroundings and to 

 accommodate ourselves to them ; to move, to talk, to hear, to see ; 

 and it guarantees equilibrium and muscular coordination. 



Divisions of the nervous system. — For purposes of study the 

 nervous system is arbitrarily divided into two parts : (1) the 

 central nervous system or cerebro-spinal system, and (2) the 

 sympathetic system. These two systems are not separate, dis- 

 tinct, and independent as the names might imply, but are inti- 

 mately connected both structurally and functionally, and are 

 really interdependent. 



(1) The central nervous system consists of the brain, the spinal 

 cord, and three sets of nerves. 



(a) Cerebro-spinal nerves connect the brain and spinal cord 

 and form a part of the cord. 



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