846 
]VIE.  HANCOCK  ON  THE  OEGANIZATION  OE  THE  BEACHIOPODA. 
the  roots  of  the  setse,  has  misled  this  distinguished  anatomist.  The  terminal  twigs  have 
been  followed,  with  the  aid  of  the  microscope,  until  from  extreme  tenuity  they  could 
no  longer  be  seen.  Had  such  a nerve  existed  it  could  hardly  have  escaped  detection. 
The  two  lateral  or  posterior  ganglia  are  fusiform,  being  elongated  in  the  antero-poste- 
rior  direction ; they  are  placed  one  at  each  side  of  the  median  line,  a little  apart  from 
each  other,  and  are  attached  by  one  extremity  to  the  posterior  margin  of  the  central 
ganglia.  These  extremities  have  the  appearance  of  being  united  across  the  middle 
line  by  a cord  or  commissure,  which  is  more  distinct  than  usual  in  W.  cranium.  The 
other  extremities  are  prolonged,  and  assuming  the  character  of  nerves,  converge  back- 
wards, and  at  the  point  where  the  wall  of  the  perivisceral  chamber  is  attached  to  the 
occlusor  muscles,  they  each  divide  into  two  trunks, — the  ventral  pallial,  and  the  posterior 
or  peduncular  nerves.  The  latter,  running  backwards,  one  on  each  side  of  the  middle 
line,  pass  from  the  parietes,  and  penetrating  these  muscles,  run  downwards  in  the  midst 
of  their  fibres ; on  reaching  their  extremities  they  turn  outwards,  and  ranning  under  the 
base  of  the  ventral  adjustor  muscle,  stretch  backwards  in  connexion  with  the  wall  of  the 
body* ; they  then  pass  one  on  each  side  of  the  peduncular  muscle  and  di\ide  into  two 
branches,  one  of  which  becoming  applied  to  the  peduncular  capsule,  supplies  it  with 
two  or  three  twigs,  which  can  be  traced  to  the  border  of  the  foramen.  This  branch  also 
gives  off  a twig,  which  is  lost  in  the  substance  of  the  peduncle.  The  other  branch  runs 
backwards  in  connexion  with  the  parietes,  and  dividing  two  or  three  times,  sends  its 
twigs  to  the  margin  of  the  foramen. 
The  pallial  nerves,  which  are  larger  than  the  peduncrdar,  pass  outwards,  running  in 
the  walls  of  the  body ; they  each  divide  immediately  into  two  portions,  both  of  which 
turning  forward  reach  the  ventral  lobe ; they  then  divide  again  four  or  five  times  dicho- 
tomously,  and  distribute  numerous  twigs  to  the  margin,  supplying  it  as  richly  as  the 
dorsal  nerve  does  the  dorsal  lobe.  The  main  branches  of  the  pallial  neiwes  of  both  lobes 
run  for  some  distance  between  the  trunks  of  the  great  pallial  sinuses,  which  they  ulti- 
mately cross  diagonally ; but  afterwards  the  branches  of  the  nerves  do  not  in  the  least 
conform  to  the  ramifications  of  the  sinuses.  Four  or  five  other  nerves  pass  from  the 
outer  side  of  the  lateral  ganglia  to  supply  the  anterior  wall  of  the  body.  Each  of  these 
takes  its  origin  by  two  or  three  delicate  roots. 
The  lateral  ganglia,  with  the  two  peduncular  nerves,  appear  to  have  escaped  notice  up 
to  this  time,  unless  two  delicate  filaments  mentioned  by  Professor  Owen**  “ as  coming  off 
from  the  lower  part  of  the  oesophageal  circle  near  to  the  origin  of  the  pallio-branchial 
trunk  ” may  be  supposed  to  represent  them,  though  they  are  more  probably  the  nerves 
which  supply  the  anterior  wall  of  the  body. 
The  central  ganglion  forms  the  under  side  of  the  collar,  and  the  cord  which  completes 
it  is  apparently  a simple  delicate  nervous  filament,  the  extremities  of  which  are  united 
to  the  ganglion,  one  at  each  side,  near  to  the  point  where  the  brachial  and  dorsal  pallial 
nerves  separate.  At  each  side  close  to  the  ganglion  the  cord  swells  a little  and  fonns  a 
* Plate  LII.  figs.  2,  3.  * Ibid. 
