﻿178 
  Mr. 
  A. 
  Sanders 
  on 
  the 
  

  

  ordinary 
  nerve-fibres. 
  The 
  axis-cylinders 
  also 
  resemble 
  those 
  

   found 
  in 
  other 
  parts 
  of 
  the 
  cord. 
  

  

  Fulliquet 
  *, 
  who 
  appears 
  to 
  have 
  been 
  the 
  first 
  to 
  investigate 
  

   microscopically 
  the 
  brain 
  of 
  Protojrterus, 
  describes 
  two 
  large 
  

   fibres 
  occupying 
  a 
  corresponding 
  position 
  in 
  the 
  spinal 
  cord 
  

   of 
  that 
  animal 
  ; 
  these 
  he 
  terms 
  Mauthner's 
  fibres, 
  but 
  from 
  

   his 
  plates 
  and 
  the 
  terms 
  in 
  which 
  he 
  mentions 
  them, 
  I 
  should 
  

   imagine 
  that 
  he 
  refers 
  to 
  Miillerian 
  fibres. 
  The 
  distinction 
  is 
  

   essential, 
  for 
  while 
  the 
  latter 
  are 
  unprovided 
  with 
  medullary 
  

   sheaths, 
  the 
  former 
  have 
  them 
  unusually 
  well-developed. 
  

  

  The 
  nerve-fibres 
  of 
  the 
  ventral 
  columns 
  do 
  not 
  so 
  mani- 
  

   festly 
  exceed 
  in 
  size 
  those 
  of 
  the 
  lateral 
  and 
  dorsal 
  columns 
  

   as 
  they 
  do 
  in 
  Teleostei, 
  consequently 
  they 
  are 
  not 
  so 
  dis- 
  

   tinctly 
  marked 
  off 
  in 
  Ceratodus 
  ; 
  the 
  larger 
  ones 
  are 
  accumu- 
  

   lated 
  more 
  towards 
  the 
  dorsal 
  edge 
  of 
  the 
  column, 
  those 
  on 
  

   the 
  ventral 
  side 
  being 
  smaller. 
  There 
  are 
  many 
  larger-sized 
  

   fibres 
  scattered 
  throughout 
  the 
  lateral 
  columns, 
  while 
  those 
  of 
  

   the 
  dorsal 
  columns 
  are 
  all 
  of 
  minute 
  dimensions. 
  

  

  The 
  ventral 
  ganglion 
  consists 
  of 
  fibrils, 
  free 
  nuclei, 
  probably 
  

   connective-tissue 
  cells, 
  and 
  nerve-cells 
  of 
  two 
  kinds 
  ; 
  the 
  

   fibrils 
  pass 
  through 
  in 
  all 
  directions 
  ; 
  many 
  are 
  continuous 
  

   with 
  the 
  fibrre 
  recta3, 
  which 
  pass 
  down 
  in 
  the 
  central 
  line 
  to 
  

   the 
  ventral 
  edge 
  of 
  the 
  cord 
  ; 
  these 
  latter 
  and 
  many 
  of 
  the 
  

   others 
  are 
  processes 
  from 
  the 
  endothelial 
  cells 
  which 
  line 
  the 
  

   central 
  canal. 
  

  

  The 
  nerve-cells 
  are 
  of 
  two 
  kinds 
  : 
  one 
  species, 
  gigantic 
  

   in 
  size 
  and 
  irregular 
  in 
  shape, 
  is 
  provided 
  with 
  numerous 
  

   branches 
  ; 
  the 
  other 
  smaller, 
  smoother 
  in 
  contour, 
  usually 
  

   gives 
  off 
  not 
  more 
  than 
  two 
  processes. 
  

  

  The 
  larger 
  species 
  (PI. 
  XII. 
  fig. 
  18) 
  are 
  generally 
  placed 
  

   at 
  the 
  inferior 
  edge 
  of 
  the 
  ventral 
  ganglion 
  ; 
  some 
  are 
  elon- 
  

   gated 
  and 
  curved, 
  following 
  the 
  outline 
  of 
  the 
  ventral 
  horn 
  

   of 
  grey 
  substance 
  ; 
  they 
  give 
  off 
  two 
  or 
  three 
  processes 
  from 
  

   each 
  end 
  and 
  four 
  or 
  five 
  from 
  their 
  convex 
  surface, 
  which 
  is 
  

   inclined 
  towards 
  the 
  white 
  substance, 
  while 
  none 
  are 
  sent 
  off 
  

   from 
  their 
  concave 
  margin, 
  which 
  embraces 
  the 
  grey 
  sub- 
  

   stance. 
  TheSe 
  cells 
  are 
  not 
  very 
  numerous 
  ; 
  sometimes 
  only 
  

   one 
  or 
  two 
  are 
  to 
  be 
  seen 
  in 
  a 
  section 
  ; 
  these 
  are 
  of 
  the 
  largest 
  

   size. 
  Occasionally 
  as 
  many 
  as 
  five 
  occur 
  in 
  one 
  section, 
  but 
  

   never 
  more 
  ; 
  in 
  this 
  case 
  they 
  are 
  smaller 
  and 
  are 
  narrow, 
  

   fusiform, 
  or 
  tripolar, 
  and 
  occupy 
  a 
  position 
  near 
  the 
  edge 
  

   and 
  also 
  sometimes 
  more 
  in 
  the 
  interior 
  of 
  the 
  ventral 
  horn. 
  

  

  The 
  processes 
  from 
  these 
  cells 
  can 
  be 
  followed 
  for 
  long 
  

   distances, 
  and 
  can 
  be 
  seen 
  to 
  give 
  off 
  branches, 
  which 
  pass 
  

   between 
  the 
  trabecular 
  network 
  which 
  forms 
  the 
  supporting 
  

   * 
  L. 
  c. 
  p. 
  48. 
  

  

  