254 
ME.  J.  L.  CLA.EKE  ON  THE  INTIMATE  STEIJCTUEE  OF  THE  BE  AIN. 
nerve, — I may  almost  affirm  that  some  at  least  are  continuous  with  the  cells.  Such  is 
the  course  I have  repeatedly  observed  in  Man ; and  in  the  Sheep  and  Ox  I can  show, 
without  any  difficulty,  that  while  some  of  the  fibres  of  the  last-mentioned  inner  bundle 
are  apparently  continuous  with  those  of  the  hypoglossal  nerve,  others  pass  inwards  to 
decussate  through  the  raphe. 
(55.)  In  Birds,  since  the  posterior  columns  are  comparatively  shallow*,  and  the  gelati- 
nous substance  is  consequently  less  advanced,  the  vagns  neiwe  is  on  a level  posterior  to 
that  in  Mammalia,  but  its  course  within  the  medulla  is  nearly  the  same ; for  the  sepa- 
rate origin  of  its  fibres  from  its  own  nucleus  and  that  of  the  h^'poglossal  neiwe,  as  well 
as  their  decussation  in  front  of  the  canal,  are  very  distinctly  and  beautifully  seen. 
(56.)  It  has  been  already  shown,  that  the  vesicular  column  that  gives  origin  to  the 
accessory  nerve,  after  reaching  the  surface  of  the  fourth  ventricle  as  the  nucleus  of  the 
A'agus,  sinks  beneath  the  auditory  ganglion,  and  diminishing  in  size,  becomes  part  of  the 
nucleus  of  the  glossopharyngeal  nerve.  Fig.  36,  Plate  XVII.  represents  exactly  a trans- 
verse section  of  one-half  of  the  human  medulla  at  the  uppeimost  roots  of  the  vagus 
nerve  (D).  {a)  is  the  restiform  body ; (v)  the  commencement  of  the  auditory  ganglion, 
formed  out  of  the  summit  of  the  posterior  pyramid,  and  apparently  of  part  of  the  vagal 
nucleus ; {b)  is  the  deep  portion  of  the  posterior  pyramid  thrown  aside  and  blending 
with  the  restiform  body : it  is  traversed  by  a network  of  fibres,  proceeding  from  the 
ganglion  of  the  portio  mollis  [v)  and  containing  a number  of  ceils,  which  send  out  their 
processes  between  the  longitudinal  bundles  represented  by  the  dark  spots ; this  netwrork 
gives  origin  to  the  anterior  or  inferior  division  of  the  auditory  nerve ; (r)  overlaid  by  the 
ganglion  of  the  portio  mollis,  and  partly  blended  with  it,  is  the  remainder  of  the  nucleus 
of  the  vagus  nerve,  enclosing  at  its  outer  extremity  its  group  of  longitudinal  bundles, 
which  now  adjoin  those  in  the  deep  portion  of  the  posterior  pyramid ; through  the  outer 
part  of  the  nucleus,  a number  of  fine  fibres,  proceeding  from  the  network  (b)  in  the 
posterior  pyramid  and  across  the  ganglion  of  the  portio  mollis,  extend  inwards  to  the 
network  in  the  lateral  column;  and  around  the  head  or  inner  extremity  of  the  vagal 
nucleus,  another  band  of  fibres,  issuing  from  the  ganglion  of  the  portio  mollis,  proceeds 
likewise  to  the  lateral  column ; [f)  is  the  extremity  of  the  posterior  cornu,  pierced 
by  longitudinal  fasciculi  and  crossed  by  the  deep  plexus  of  arciform  fibres  proceeding 
from  the  posterior  pyramid  and  the  restiform  body ; along  its  inner  or  anterior  margin 
(^)  a bundle  of  fibres  and  a blood-vessel  extends  forwards  and  outw*ards  through  the 
lateral  column,  and  more  internally  are  two  or  three  others,  running  in  the  same  direc- 
tion ; (i^)  is  the  floor  of  the  fourth  ventricle ; it  is  continuous  with  that  of  the  central 
canal,  and  is  likewise  lined  with  columnar  epithelium,  which  rests  on  a layer  of  fine  fibres. 
Beneath  the  latter  is  another  layer  of  fibres  {d),  interspersed  on  each  side,  and  partly  con- 
tinuous, with  a number  of  oval  cells,  which  lie  with  their  longer  axes  parallel  to  them ; 
in  their  course  inwards  the  fibres  run  down  the  side  of  the  raphe  [f),  and  in  the  opposite 
direction  they  extend  round  the  surface  of  the  auditory  ganglion.  Immediately  beneath 
this  layer,  and  resting  on  the  inner  part  of  the  antero-lateral  column,  is  the  continuation 
