KERYOUS SYSTEM AND GENERAL SENSATION. 



33 



terised by the double contour, than those of the peripheral 

 fibres. In the central fibres, too, the sheath and contents appear 

 to be far more intimately connected ; in many cases they are 

 completely inseparable, so that the contrast as betwixt sheath 

 and contents disappears. These delicate primary fibrils of 

 the central masses run in such a variety of ways, crossing and 

 interlacing, and forming such a tangled skein, that it is 

 impossible to follow them to the roots of the nerves, or towards 

 the periphery of the brain and cord, and so to make certain 

 that they never anastomose. To all appearance, however, they 



Fig. 12. A small portion of the terminal plexus of primary fibres of the 

 auditory nerve in the auditory sac of the pike (Esox lucius.) 



