CHAPTER IX. 



THE NERVOUS SYSTEM. 



The Brain, Spinal Marrow, and Nerves, 



1. THERE is no subject, which falls within the range of 

 physiological enquiry, more interesting or more important, 

 than that of the nervous system, tt is this which furnishes 

 the material instrument of thought, the means by which we 

 become acquainted with the external world around us, and 

 also the channels by which the will sends forth its commands 

 to the instruments it employs in their execution.) Besides 

 this, it presides over and regulates the functions of the ani- 

 mal economy, and binds the various organs into one sympa- 

 thizing, harmonious whole. 



2. The nervous system may be considered as embracing, 

 1st. the brain ; 2d. the medulla oblongata ; 3d. the spinal 

 marrow ; 4th. the nerves ; 5th. th ganglia. These are all 

 embraced under two general departments, the first consisting 

 of the brain and its dependencies ; and the second, of the 

 ganglia and their nervous connections pi the first appertain- 

 ing particularly to animal life, conveying impressions calcu- 

 lated to produce sensations, and sending out volitions to its 

 servants, the organs destined to receive them ; while the 

 second supply those organs not under the influence of the 

 will, viz. of digestion, circulation, respiration, and the secre- 

 tions. 



3. (These two grand divisions of the nervous system, 

 may be still further distinguished by the circumstance, that 

 the first, or cerebral department, is exactly symmetrical! 

 The nerves all go out in pairs from each side of fhe brain 

 and spinal cord, while the ganglionic system of nerves is dis- 

 tributed irregularly to all the internal organs. The nerves 



