﻿60 
  W. 
  13. 
  HANDLES. 
  

  

  to 
  the 
  anterior 
  thickened 
  margin 
  of 
  the 
  mantle, 
  where 
  they 
  

   eventually 
  unite 
  with 
  one 
  another, 
  forming 
  a 
  circumpallial 
  

   anastomosis 
  (Pelseueer, 
  36, 
  p. 
  50). 
  The 
  posterior 
  branch 
  

   of 
  the 
  pallial 
  nerve 
  is 
  distributed 
  to 
  the 
  posterior 
  portion 
  of 
  

   the 
  mantle 
  which 
  ensheathes 
  the 
  columella 
  muscle. 
  In 
  

   addition 
  to 
  the 
  pallial 
  nerve 
  a 
  collumella 
  nerve 
  is 
  given 
  off 
  

   from 
  the 
  pleural 
  ganglion. 
  

  

  Visceral 
  Commissure. 
  — 
  The 
  right 
  or 
  supra-intestinal 
  

   branch 
  (fig. 
  30, 
  sp. 
  int.) 
  of 
  the 
  visceral 
  loop 
  arises 
  from 
  the 
  

   right 
  pleural 
  ganglion 
  slightly 
  in 
  front 
  of 
  the 
  pallial 
  nerve 
  of 
  

   this 
  side. 
  It 
  passes 
  upwards 
  over 
  the 
  odontophore 
  and 
  

   through 
  a 
  fold 
  in 
  the 
  dorsal 
  wall 
  of 
  the 
  crop 
  to 
  the 
  left 
  side 
  

   of 
  the 
  body, 
  where 
  it 
  penetrates 
  the 
  body-wall. 
  Here 
  it 
  gives 
  

   origin 
  to 
  two 
  nerves, 
  one 
  going 
  to 
  the 
  large 
  branchial 
  

   ganglion 
  {bn. 
  g.) 
  which 
  is 
  situated 
  at 
  the 
  base 
  of 
  the 
  gill, 
  the 
  

   other 
  nerve 
  [d.) 
  running 
  to 
  and 
  anastomosing 
  with 
  the 
  left 
  

   pallial 
  nerve, 
  thus 
  presenting 
  a 
  condition 
  of 
  dialyneury 
  on 
  

   the 
  left 
  side 
  of 
  the 
  body. 
  At 
  the 
  point 
  of 
  origin 
  of 
  these 
  two 
  

   nerves 
  there 
  is 
  a 
  slight 
  enlargement 
  and 
  concentration 
  of 
  

   nerve-cells, 
  and 
  we 
  can 
  consequently 
  look 
  upon 
  this 
  centre 
  as 
  

   representing 
  the 
  supra-intestinal 
  ganglion, 
  though 
  it 
  is 
  by 
  no 
  

   means 
  so 
  large 
  or 
  so 
  clearly 
  defined 
  as 
  delineated 
  by 
  Pelseneer 
  

   (36, 
  pi. 
  xvii, 
  fig. 
  148). 
  The 
  branchial 
  ganglion 
  innervates 
  

   both 
  the 
  gill 
  and 
  the 
  osphradium. 
  The 
  supra-intestinal 
  

   branch 
  of 
  the 
  visceral 
  commissure 
  then 
  continues 
  its 
  course 
  

   along 
  the 
  left 
  side 
  of 
  the 
  mantle-cavity, 
  situated 
  in 
  the 
  angle 
  

   between 
  the 
  body-wall 
  and 
  the 
  gill, 
  it 
  runs 
  parallel 
  to 
  the 
  

   latter 
  structure 
  until 
  it 
  reaches 
  the 
  level 
  of 
  the 
  papillary 
  sac, 
  

   where 
  it 
  crosses 
  the 
  body 
  from 
  left 
  to 
  right, 
  passing 
  above 
  

   the 
  oesophagus 
  and 
  intestine, 
  and 
  terminating 
  in 
  the 
  abdominal 
  

   ganglion 
  {ah. 
  g.) 
  which 
  is 
  situated 
  under 
  the 
  epithelium 
  of 
  

   the 
  floor 
  of 
  the 
  mantle-cavity. 
  

  

  The 
  subintestinal 
  branch 
  (fig. 
  30, 
  suh. 
  int.) 
  of 
  the 
  visceral 
  

   loop 
  arises 
  from 
  the 
  left 
  pleural 
  ganglion 
  by 
  a 
  trunk 
  common 
  

   to 
  both 
  this 
  nerve 
  and 
  the 
  left 
  pallial 
  nerve 
  ; 
  it 
  then 
  passes 
  

   underneath 
  the 
  oesophagus 
  and 
  radula-sac, 
  and 
  continues 
  its 
  

   course 
  on 
  the 
  right 
  side 
  of 
  the 
  body 
  between 
  the 
  oesophagus 
  

  

  