﻿Nervous 
  System 
  of 
  Geratodus 
  Forsteri. 
  183 
  

  

  Patheticus 
  (PI. 
  XI. 
  fig. 
  9, 
  n. 
  4). 
  — 
  The 
  trunk 
  of 
  this 
  nerve 
  

   was 
  not 
  discovered, 
  but 
  that 
  it 
  exists 
  is 
  shown 
  by 
  the 
  fact 
  

   that 
  its 
  decussation 
  and 
  part 
  of 
  its 
  course 
  and 
  exit 
  is 
  to 
  be 
  

   seen 
  in 
  the 
  transverse 
  section 
  of 
  the 
  valve 
  of 
  Vieussens, 
  that 
  

   is 
  to 
  say, 
  in 
  the 
  connecting-link 
  between 
  the 
  cerebellum 
  and 
  

   the 
  optic 
  lobe. 
  

  

  Trifacial 
  (PI. 
  X. 
  fig. 
  11, 
  n. 
  5). 
  — 
  The 
  anterior 
  root 
  of 
  the 
  

   trifacial 
  is 
  derived 
  from 
  a 
  ganglion 
  situated 
  at 
  the 
  external 
  

   edge 
  of 
  the 
  floor 
  of 
  the 
  fourth 
  ventricle, 
  where 
  it 
  forms 
  a 
  flat 
  

   broad 
  swelling, 
  which 
  occupies 
  the 
  space 
  between 
  the 
  ridge 
  of 
  

   the 
  ventral 
  column 
  and 
  the 
  corpus 
  restiforme 
  ; 
  this 
  swelling 
  

   is 
  visible 
  on 
  macroscopic 
  inspection 
  ; 
  from 
  this 
  ganglion 
  the 
  

   fibres 
  proceed 
  directly 
  downward 
  and 
  outward 
  to 
  emerge 
  at 
  

   the 
  inferior 
  external 
  angle 
  of 
  the 
  medulla 
  oblongata 
  ; 
  it 
  corre- 
  

   sponds 
  to 
  the 
  anterior 
  origin 
  in 
  Teleostei, 
  but 
  the 
  root 
  has 
  a 
  

   more 
  direct 
  course 
  to 
  its 
  exit. 
  

  

  The 
  posterior 
  roots 
  of 
  the 
  trifacial 
  have 
  a 
  single 
  origin, 
  

   which 
  divides 
  into 
  two 
  trunks 
  immediately 
  outside 
  the 
  brain. 
  

   The 
  origin 
  is 
  from 
  the 
  tuberosity 
  on 
  the 
  summit 
  of 
  the 
  resti- 
  

   form 
  bodies, 
  constituting 
  part 
  of 
  the 
  continuation 
  of 
  the 
  

   molecular 
  layer 
  of 
  the 
  cerebellum, 
  which 
  passes 
  on 
  to 
  those 
  

   bodies 
  where 
  the 
  crura 
  cerebelli 
  are 
  detached 
  ; 
  there 
  are 
  here 
  

   a 
  few 
  medium-sized 
  cells 
  from 
  which 
  its 
  fibres 
  might 
  be 
  de- 
  

   rived, 
  but 
  it 
  is 
  principally 
  composed 
  of 
  somewhat 
  coarsely 
  

   granular 
  neuroglia 
  and 
  numerous 
  fibrils. 
  A 
  bundle 
  of 
  fibres 
  

   (PI. 
  XII. 
  fig. 
  12) 
  from 
  this 
  tuberosity 
  passes 
  down 
  the 
  inner 
  

   margin 
  of 
  the 
  restiform 
  body, 
  crosses 
  the 
  origin 
  of 
  the 
  facial, 
  

   and 
  is 
  lost 
  in 
  the 
  field 
  of 
  the 
  medulla 
  oblongata 
  with 
  the 
  trans- 
  

   verse 
  commissure 
  which 
  occupies 
  that 
  part. 
  

  

  Facial 
  (PI. 
  XII. 
  fig. 
  12, 
  n. 
  7). 
  — 
  This 
  nerve 
  passes 
  into 
  the 
  

   cord 
  at 
  the 
  inferior 
  external 
  angle 
  in 
  an 
  upward 
  and 
  inward 
  

   direction 
  until 
  it 
  reaches 
  the 
  angle 
  formed 
  between 
  the 
  floor 
  

   and 
  the 
  walls 
  of 
  the 
  fourth 
  ventricle, 
  at 
  which 
  point 
  one 
  part 
  

   of 
  it 
  passes 
  backward 
  as 
  a 
  well-defined 
  bundle 
  in 
  a 
  small 
  

   tuberosity, 
  in 
  which 
  it 
  can 
  be 
  traced 
  backward 
  for 
  a 
  long 
  

   distance, 
  and 
  is 
  eventually 
  lost 
  in 
  the 
  grey 
  matter 
  of 
  the 
  

   tuberosity 
  at 
  about 
  the 
  middle 
  of 
  the 
  ventricles. 
  

  

  The 
  remainder 
  of 
  this 
  nerve 
  has 
  a 
  more 
  direct 
  origin 
  from 
  

   the 
  grey 
  matter 
  of 
  the 
  lower 
  part 
  of 
  the 
  wall 
  of 
  the 
  ventricle, 
  

   beyond 
  which 
  this 
  part 
  cannot 
  be 
  traced. 
  

  

  Acusticus 
  (PI. 
  XII. 
  fig. 
  12, 
  n. 
  8). 
  — 
  This 
  nerve, 
  arising 
  

   below 
  the 
  facial, 
  passes 
  obliquely 
  upward 
  and 
  inward 
  until 
  it 
  

   reaches 
  the 
  floor 
  of 
  the 
  fourth 
  ventricle 
  at 
  a 
  point 
  some 
  dis- 
  

   tance 
  internal 
  to 
  the 
  facial. 
  On 
  attaining 
  the 
  grey 
  matter 
  of 
  

   the 
  floor 
  of 
  the 
  ventricle 
  (" 
  Bodengrau 
  ; 
  ' 
  of 
  German 
  authors) 
  

   it 
  turns 
  towards 
  the 
  mid 
  line 
  until 
  it 
  arrives 
  at 
  the 
  margin 
  of 
  

  

  