3i6 Elementary Biology. 



cylinders of nerve-fibres. The cells are naked, and the 

 sheaths of the nerve cease before uniting with the nerve- 

 cell. 



Before leaving the nervous system it will be necessary to 

 indicate briefly the functions of the various parts of that 

 system. The brain, as a whole, may be looked upon as 

 the grand centre for the originating and governing of the 



FIG. 173. MULTIPOLAR NERVE-CELL. (Schafer.) 



various actions of the body, as well as for the reception of 

 all impressions derived from the body itself or from the 

 external world ; whilst the nerves are the organs for trans- 

 mitting these impulses and impressions from and to the brain, 

 or sensorium. A little reflection will enable us to analyse 

 the nervous messages into at least two chief classes 

 centrifugal or motor impulses, and centripetal or sensory 

 impulses. To these, however, we must add impulses of at 



