﻿186 
  

  

  Mr. 
  A. 
  Sanders 
  on 
  the 
  

  

  of 
  dissimilarity 
  in 
  the 
  greater 
  part 
  of 
  their 
  course 
  ; 
  yet 
  at 
  their 
  

   anterior 
  end 
  they 
  show 
  a 
  similarity 
  both 
  in 
  their 
  appearance 
  

   Avhen 
  only 
  one 
  axis-cylinder 
  remains 
  enclosed 
  in 
  the 
  medullary 
  

   sheath, 
  and 
  also 
  in 
  the 
  fact 
  of 
  their 
  decussation 
  and 
  in 
  the 
  

   position 
  of 
  that 
  decussation. 
  

  

  With 
  Petromyzon 
  the 
  only 
  points 
  of 
  contact 
  are 
  the 
  tela 
  

   choroidea, 
  which 
  covers 
  in 
  the 
  fourth 
  ventricle, 
  and 
  the 
  multi- 
  

   axial 
  fibre 
  ; 
  the 
  tela 
  choroidea 
  appears 
  to 
  have 
  the 
  same 
  sort 
  

   of 
  structure, 
  and 
  if 
  my 
  supposition 
  be 
  correct 
  the 
  multiaxial 
  

   fibre 
  represents 
  a 
  more 
  advanced 
  stage 
  of 
  development 
  of 
  the 
  

   Miillerian 
  fibres. 
  

  

  With 
  regard 
  to 
  the 
  other 
  division 
  of 
  the 
  class 
  Ichthyopsida, 
  

   viz. 
  the 
  Amphibia, 
  there 
  seem 
  to 
  be 
  as 
  many 
  points 
  of 
  difference 
  

   as 
  agreement, 
  so 
  that 
  from 
  the 
  point 
  of 
  view 
  of 
  the 
  structure 
  

   of 
  the 
  nervous 
  system 
  Ceratodus 
  appears 
  to 
  be 
  quite 
  isolated, 
  

   and 
  while 
  presenting 
  some 
  agreement 
  in 
  structure 
  with 
  all 
  the 
  

   members 
  of 
  the 
  class 
  Pisces, 
  is 
  nearly 
  related 
  to 
  no 
  one 
  of 
  

   them. 
  

  

  EXPLANATION 
  OF 
  PLATES 
  VIII. 
  -XIII. 
  

  

  The 
  following 
  letters 
  have 
  the 
  same 
  signification 
  throughout 
  : 
  — 
  

  

  f.a 
  

  

  a. 
  c. 
  Anterior 
  commissure. 
  

   aq. 
  sy. 
  Aqueduct 
  of 
  Sylvius. 
  

  

  b. 
  Nervi 
  branchiales. 
  

  

  b. 
  ce. 
  Inferior 
  bulla 
  of 
  the 
  cerebrum. 
  

  

  c. 
  a. 
  Oommissura 
  ausulata. 
  

   c. 
  c. 
  Crura 
  cerebri. 
  

  

  c. 
  ca. 
  Central 
  canal 
  of 
  the 
  spinal 
  

   cord. 
  

  

  c. 
  cbl. 
  Crura 
  cerebelli 
  ad 
  medullam. 
  

  

  cbl. 
  Cerebellum. 
  

  

  ce. 
  Cerebral 
  lobes. 
  

  

  c. 
  g. 
  Cells 
  of 
  the 
  central 
  ganglion. 
  

  

  ch. 
  op. 
  Chiasma 
  nervorum 
  opti- 
  

   corum. 
  

  

  ch. 
  te. 
  Tela 
  choroidea. 
  

  

  co. 
  Communicating 
  branch 
  between 
  

   the 
  trifacial 
  and 
  the 
  vagus. 
  

  

  co. 
  p. 
  Communicating 
  branch 
  be- 
  

   tween 
  the 
  glossopharyngeal 
  

   and 
  vagus 
  ganglion. 
  

  

  c. 
  v. 
  g. 
  Cells 
  of 
  the 
  ventral 
  gan- 
  

  

  glion. 
  

  

  d. 
  h. 
  Dorsal 
  horn 
  of 
  the 
  grey 
  sub- 
  

  

  stance. 
  

   d. 
  I. 
  Dorsal 
  longitudinal 
  columns. 
  

  

  d. 
  r. 
  Dorsal 
  roots 
  of 
  the 
  spinal 
  

  

  nerves. 
  

  

  e. 
  Epiphysis. 
  

  

  Fibres 
  belonging 
  to 
  the 
  acus- 
  

   ticus. 
  

  

  f.f. 
  Fasciculus 
  of 
  the 
  root 
  of 
  the 
  

   facial 
  nerve. 
  

  

  f. 
  1. 
  Fibrous 
  layer 
  of 
  the 
  cerebel- 
  

   lum. 
  

  

  ff. 
  I. 
  Granular 
  layer 
  of 
  the 
  cerebel- 
  

   lum. 
  

  

  (jl. 
  o. 
  Glomeruli 
  olfactorii. 
  

  

  (jn. 
  h. 
  Ganglion 
  Habenuhe 
  or 
  tu- 
  

   berculum 
  intermedium. 
  

   r. 
  op. 
  Ganglion 
  of 
  the 
  roof 
  of 
  

   the 
  optic 
  lobe. 
  

  

  th. 
  Ganglion 
  of 
  the 
  thalamen- 
  

   cephalon. 
  

  

  gn. 
  tri. 
  Ganglion 
  of 
  the 
  trifacial. 
  

  

  gn. 
  v. 
  Ganglion 
  of 
  the 
  vagus. 
  

  

  i. 
  I. 
  Internal 
  layer 
  of 
  the 
  olfactory 
  

   lobe. 
  

  

  i. 
  m. 
  Inferior 
  maxillary 
  nerve. 
  

  

  in. 
  Infundibuluni. 
  

  

  I. 
  c. 
  Lateral 
  columns 
  of 
  the 
  cord. 
  

  

  m. 
  Combined 
  superior 
  and 
  inferior 
  

   maxillary 
  nerve. 
  

  

  in. 
  ce. 
  Mesencephalon. 
  

  

  in. 
  I. 
  Molecular 
  layer 
  of 
  the 
  cere- 
  

   bellum. 
  

  

  mlt. 
  Multiaxial 
  fibre. 
  

  

  gn. 
  

  

  gn. 
  

  

  