﻿180 
  Mr. 
  A. 
  Sanders 
  on 
  the 
  

  

  Occasionally 
  axis-cylinders 
  may 
  be 
  seen 
  escaping 
  singly 
  or 
  

   in 
  groups, 
  passing 
  through 
  the 
  medullary 
  sheath, 
  without 
  

   diminution 
  of 
  size, 
  into 
  the 
  field 
  of 
  the 
  ventral 
  columns. 
  This 
  

   fact 
  accounts 
  for 
  the 
  diminution 
  of 
  size 
  at 
  various 
  points 
  in 
  

   the 
  course 
  of 
  the 
  fibres. 
  

  

  The 
  shape 
  of 
  the 
  multiaxial 
  fibres 
  varies 
  according 
  to 
  the 
  

   part 
  of 
  the 
  spinal 
  cord 
  in 
  which 
  they 
  are 
  observed 
  ; 
  at 
  the 
  

   posterior 
  end 
  they 
  are 
  elliptical, 
  towards 
  the 
  centre 
  they 
  are 
  

   round, 
  and 
  further 
  forward 
  they 
  are 
  almond-shaped. 
  

  

  Some 
  distance 
  behind 
  its 
  anterior 
  termination 
  (PL 
  X. 
  fig. 
  13) 
  

   one 
  axis-cylinder 
  has 
  become 
  distinguished 
  from 
  the 
  remainder 
  

   by 
  its 
  greater 
  consistency, 
  and 
  by 
  its 
  taking 
  the 
  staining-fluid 
  

   more 
  readily 
  ; 
  in 
  some 
  places 
  it 
  becomes 
  clothed 
  with 
  a 
  special 
  

   medullary 
  sheath, 
  which, 
  however, 
  soon 
  disappears 
  and 
  is 
  not 
  

   visible 
  in 
  every 
  specimen. 
  

  

  At 
  a 
  short 
  distance 
  posterior 
  to 
  the 
  point 
  where 
  the 
  facial 
  

   emerges 
  from 
  the 
  brain 
  this 
  axis-cylinder 
  is 
  the 
  only 
  one 
  

   remaining, 
  all 
  the 
  others 
  having 
  disappeared, 
  the 
  whole 
  fibre 
  

   having 
  in 
  the 
  meantime 
  gradually 
  diminished 
  in 
  size. 
  The 
  

   fibre 
  has 
  now 
  quite 
  the 
  appearance 
  of 
  the 
  Mauthner's 
  fibre 
  of 
  

   the 
  Teleostei, 
  consisting 
  as 
  it 
  does 
  at 
  this 
  point 
  of 
  a 
  single 
  

   large 
  axis-cylinder 
  surrounded 
  by 
  a 
  thick 
  medullary 
  sheath. 
  

   Immediately 
  in 
  front 
  of 
  this 
  spot 
  the 
  axis-cylinder 
  of 
  one 
  side 
  

   decussates 
  with 
  that 
  of 
  the 
  other, 
  the 
  place 
  corresponding 
  with 
  

   the 
  position 
  of 
  the 
  decussation 
  of 
  the 
  Mauthner's 
  fibres 
  in 
  the 
  

   Teleostei. 
  After 
  the 
  decussation 
  the 
  two 
  axis-cylinders, 
  still 
  

   surrounded 
  by 
  the 
  medullary 
  sheath, 
  are 
  to 
  be 
  seen 
  pursuing 
  

   a 
  course 
  beneath 
  the 
  floor 
  of 
  the 
  fourth 
  ventricle 
  towards 
  the 
  

   external 
  edge, 
  and 
  can 
  be 
  traced, 
  with 
  the 
  exception 
  of 
  a 
  very 
  

   small 
  gap, 
  into 
  the 
  root 
  of 
  the 
  facial. 
  Fulliquet 
  * 
  describes 
  

   a 
  decussation 
  of 
  the 
  fibres 
  which 
  he 
  terms 
  " 
  Mauthner's 
  " 
  at 
  

   a 
  corresponding 
  place 
  in 
  Protopterus 
  ; 
  but 
  their 
  destination 
  

   according 
  to 
  him, 
  although 
  he 
  does 
  not 
  appear 
  to 
  be 
  quite 
  

   certain 
  on 
  the 
  point, 
  is 
  somewhat 
  different, 
  as 
  he 
  says 
  that 
  

   they 
  go 
  to 
  the 
  sixth 
  root 
  of 
  the 
  acusticus. 
  While 
  the 
  multi- 
  

   axial 
  fibre 
  is 
  diminishing 
  in 
  size 
  its 
  place 
  in 
  the 
  ventral 
  

   column 
  is 
  taken 
  by 
  an 
  increasing 
  number 
  of 
  fibres, 
  which 
  are 
  

   most 
  probably 
  the 
  axes 
  that 
  have 
  escaped 
  from 
  that 
  body 
  ; 
  

   their 
  destination, 
  as 
  will 
  appear 
  presently, 
  is 
  to 
  form 
  part 
  of 
  

   the 
  root 
  of 
  the 
  acusticus. 
  

  

  In 
  seeking 
  for 
  the 
  signification 
  of 
  these 
  multiaxial 
  fibres 
  it 
  

   will 
  be 
  as 
  well 
  to 
  consider 
  what 
  nerve-fibres 
  other 
  nearly- 
  

   related 
  animals 
  possess. 
  We 
  have 
  in 
  Teleostei 
  the 
  well- 
  

   known 
  Mauthner's 
  fibres, 
  which 
  occupy 
  a 
  corresponding 
  

  

  * 
  Z. 
  c. 
  p. 
  82. 
  

  

  