﻿102 
  

  

  E. 
  J. 
  ALLEN. 
  

  

  (m. 
  h.), 
  it 
  being 
  probably 
  here 
  tliat 
  the 
  fibres 
  of 
  the 
  couimis- 
  

   sures 
  from 
  the 
  two 
  sides 
  cross 
  each 
  other. 
  From 
  this 
  region 
  

   the 
  fibres 
  pass 
  first 
  forwards 
  and 
  downwards 
  and 
  then 
  turn 
  

   outwards, 
  after 
  which, 
  in 
  sagittal 
  sections, 
  they 
  form 
  a 
  circular 
  

   patch 
  of 
  traDsversly 
  cut 
  fibres 
  {comm.), 
  which 
  can 
  be 
  easily 
  

   followed 
  through 
  the 
  brain 
  substance. 
  Arising 
  from 
  the 
  

   same 
  central 
  mass 
  of 
  punctated 
  substance 
  {m. 
  h.), 
  but 
  at 
  a 
  

   level 
  external 
  to 
  that 
  at 
  which 
  the 
  fibres 
  of 
  the 
  commissures 
  

   leave 
  it, 
  a 
  bundle 
  of 
  fibres 
  can 
  be 
  traced, 
  which 
  passes 
  

   forwards 
  and 
  downwards 
  into 
  the 
  epithelium 
  in 
  front 
  of 
  the 
  

   brain, 
  from 
  whence 
  it 
  can 
  be 
  easily 
  followed 
  as 
  a 
  well-marked 
  

  

  mb 
  

  

  ant 
  

  

  ,post 
  gang 
  cells 
  

  

  Pig. 
  1. 
  — 
  Diagrammatic 
  sagittal 
  section 
  througli 
  one 
  side 
  of 
  tlie 
  brain 
  

   of 
  Pcecilochai'us. 
  ant. 
  gang, 
  cells, 
  anterior 
  ganglion 
  cells 
  ; 
  n. 
  A, 
  

   nerve 
  to 
  mediau 
  tentacle 
  ; 
  comm., 
  oesophageal 
  commissure; 
  «. 
  p. 
  1, 
  

   anterior 
  root 
  of 
  nerve 
  to 
  palp-ganglion 
  ; 
  n. 
  p. 
  2, 
  posterior 
  ditto 
  ; 
  

   n.p. 
  G., 
  nerve 
  to 
  pa.\\)-^Rng\ion 
  ; 
  posl. 
  gang, 
  cells, 
  posterior 
  ganglion- 
  

   cells 
  ; 
  m. 
  b., 
  central 
  mass 
  of 
  fibres 
  from 
  which 
  oesophageal 
  com- 
  

   missures 
  and 
  tentacle 
  nerve 
  arise; 
  n.n.g., 
  nerve 
  to 
  nuchal 
  

   ganglion. 
  

  

  nerve 
  (7^. 
  t.) 
  to 
  the 
  median 
  tentacle, 
  which 
  lies 
  just 
  in 
  front 
  of 
  

   the 
  mouth 
  (cf. 
  PI. 
  11, 
  fig. 
  42). 
  The 
  bundle 
  of 
  fibres 
  just 
  

   described 
  exists 
  on 
  each 
  side 
  of 
  the 
  brain, 
  and 
  two 
  nerves, 
  one 
  

   from 
  each 
  side, 
  can 
  be 
  followed 
  with 
  perfect 
  certainty 
  from 
  

   the 
  centre 
  of 
  the 
  brain 
  to 
  the 
  single 
  mediau 
  tentacle. 
  

  

  From 
  about 
  the 
  middle 
  of 
  the 
  ventral 
  surface 
  of 
  the 
  brain 
  

   on 
  each 
  side 
  a 
  bundle 
  of 
  fibres 
  arises 
  (n.p. 
  1) 
  which 
  passes 
  

   backwards. 
  This 
  bundle 
  of 
  fibres 
  is 
  subsequently 
  joined 
  by 
  

   a 
  second 
  bundle 
  {n.p. 
  2), 
  which 
  leaves 
  the 
  brain 
  at 
  its 
  

  

  