356 THE SOLIDS. 



ART. XIX. NERVES. 



THE nervous system has been divided into two orders or 

 lesser systems ; the cerebro-spinal, which includes the brain 

 and spinal cord, together with the nerves which proceed 

 therefrom, and the sympathetic systems. The former, 

 which admits of still further leading divisions, presides over 

 animal life, its nerves administering to sensation, and being 

 distributed to the principal organs of locomotion, the muscles, 

 as well as to those of the senses ; the latter is connected with 

 the functions of organic life, and supplies principally the 

 viscera and glands with nerves. 



Corresponding with the presumed functional differences of 

 the two systems, there are also certain structural differences, 

 the nature of which will shortly be described. 



STRUCTURE OF NERVES. 



CEREBRO-SPINAL SYSTEM. The nervous matter consti- 

 tuting the cerebro-spinal system consists of two very di&tinct 

 substances, a grey, cineritious, cellular, or secreting structure, 

 and a white, conducting, or tubular structure. 



Secreting or Cellular Structure. The very numerous situ- 

 ations in which the grey matter of the brain and spinal cord 

 is encountered need not here be described at any length : it 

 will be sufficient to observe, that in the cerebrum it oc- 

 cupies principally an external situation, a layer of it of 

 about the one-eighth of an inch in thickness, extending over 

 the entire surface of its convolutions ; but that it is also 

 found in lesser quantities in several localities in the interior 

 of the cerebrum, as in the optic thalami, corpora striata, 

 tuber cinerium, crura cerebri, &c. ; that on the other hand, 

 in the cerebellum, pons Varollii, medulla oblongata, and 



