CH. XVII.] 



WHITE AND GREY MATTER 



191 



White matter is composed of medullated nerve-fibres, which differ 

 in structure from the medul- 

 lated fibres of nerve by 

 having no primitive sheath 

 (neurilemma). 



Grey matter is the true 

 central material so far as re- 

 gards function; that is to 

 say, it is the part which 

 receives and sends out 

 nervous impulses ; it is 

 characterised by containing 

 the bodies of the nerve- 

 cells. 



In the brain the grey 

 matter is chiefly situated 

 on the surface, forming 

 what is called the cortex; 

 the white matter and cer- 

 tain subsidiary masses of 

 grey matter are in the 

 interior. 



In the spinal cord, the 

 grey matter is in the in- 

 terior, the white matter 

 outside. 



In both grey and white 

 matter the nerve-cells and 

 nerve-fibres are supported 

 by a peculiar tissue which 

 is called neuroglia. It is 

 composed of cells and fibres, 

 the latter being prolonged 

 from the cells. Some of the 

 fibres are radially arranged. 

 They start from the outer 

 ends of the ciliated epithe- 

 lium cells that line the 

 central canal of the spinnl 

 cord and the ventricles of 

 the brain, and diverge con- 

 stantly branching towards 

 the surface of the organ, 

 where they end by slight 

 enlargements attached to 



FIG. 203. View of the cerebro-spinal axis of the iiervous 

 system. The right half of the cranium and trunk of 

 the body has been removed by a vertical section ; the 

 membranes of the brain and spinal cord have also been 

 removed, and the roots and first part of the fifth and 

 ninth cranial, and of all the spinal nerves of the right 

 side, have been dissected out and laid separately on the 

 wall of the skull and on the several vertebrae opposite 

 to the place of their natural exit from the cranio-spinal 

 cavity. (After Bourgery.) 



