376 



THE NERVOUS SYSTEM. 



by degrees assuming the characters of the nerve-fibre with 

 which it is continuous. 



c D E 



Various forms of ganglionic vesicles : A, B, large stellate cells, with their prolon- 

 gations, from the anterior horn of the gray matter of the spinal cord ; c, nerve-cell 

 with its connected fibre, from the anastomosis of the facial and auditory nerves in 

 the meatus auditorius internus of the ox ; a, cell-wall ; b, cell-contents; c, pigment; 

 d, nucleus ; e, prolongation forming the sheath of the fibre ; /, nerve-fibre ; D, nerve- 

 cell from the substantia ferruginea of man ; E, smaller cell from the spinal cord, 

 magnified 350 diameters. 



Functions of Nerve-Fibres. 



The office of the nerves as simple conveyers or conductors 

 of nervous impressions is of a twofold kind. First, they serve 

 to convey to the nervous centres the impressions made upon 

 their peripheral extremities, or parts of their course. Sec- 

 ondly, they serve to transmit impressions from the brain and 

 other nervous centres to the parts to which the nerves are 

 distributed. 



For this twofold office of the nerves, two distinct sets of 

 nerve-fibres are provided, in both the cerebro-spinal and sym- 

 pathetic systems. Those which convey impressions from the 

 periphery to the centre are classed together as centripetal or 

 afferent nerves. Those fibres, on the other hand, which are 

 employed to transmit central impulses to the periphery are 

 classed as centrifugal or efferent nerves. 



Centripetal or afferent nerve-fibres may (a) convey to the 

 nerve-centres with which they are connected impressions which 



