NERVOUS SYSTEM. 



CHAPTER FOURTH. 



NERVOUS SYSTEM, OR ORGANS OF SENSIBILITY AND 

 MOTILITY. 



FIRST SECTION. 



General Observations on the Nervous System. 



THE nervous system communicates to the muscles their 

 energy of action, and to all the sentient parts of the body 

 their power of feeling. By the rapidity of its action, and its 

 extensive distribution through the body, it establishes an in- 

 stantaneous communication between the most distant parts. 

 It is chiefly by this system that animals are connected with 

 surrounding nature, and there is no part of their economy 

 which is more indicative than this of the condition of the 

 whole organization, or of the grade which an animal occupies 

 in the scale. The nervous system has been detected in every 

 division of the animal kingdom, and almost in every class, 

 and it is everywhere connected with sensation and motion. 

 Its general form corresponds with that of the body, being short 

 and disposed in a circular manner in the short round bodies 

 of most of the radiated and molluscous animals, and having a 



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