232 
ME.  J.  L.  CLAEKE  ON  THE  INTIIVIATE  STEUCTUEE  OE  THE  BEAIN. 
tnedulla  oblongata  is  generally  understood  to  extend  from  near  the  points  of  the  anterior 
l)yrarmds  to  the  lower  border  of  \he  pons,  and  as  such  it  is  described  in  this  memoir. 
(2.)  It  is  well  known  that  in  the  spinal  chord  the  columns  of  white  and  grey  substance 
are  parallel  to  each  other,  and  preserve  the  same  relative  position  throughout  their  entire 
course ; but  in  the  medulla  oblongata  these  parts  not  only  assume  a different  an*ange- 
ment,  by  becoming  more  or  less  blended  with  each  other  and  with  new  stmctures,  but 
frequently  pursue  a curvilinear  direction  in  different  planes  inclined  at  varying  angles. 
It  is  evident,  therefore,  that  transverse  and  longitudinal  sections,  however  transparent 
they  may  be  made,  must  be  insufficient,  when  employed  alone,  to  complete  the  exami- 
nation of  so  intricate  a structure.  For  this  reason,  after  having  made  myseK  thoroughly 
acquainted  with  the  microscopical  anatomy  of  these  parts,  and  traced  their*  relations  and 
corrnexions,  as  far  as  possible,  by  my  own  method  of  preparation,  which  I find  superior 
to  any  other  that  I have  seen  of  the  same  kind,  I then  employed,  in  conjunction  with 
it,  the  method  of  Keil;  so  that  when  necessary,  the  strrrcture  revealed  at  different 
stages  of  the  dissection  was  compared  with  transparent  sections  through  the  same  parts. 
Great  assistance  was  also  obtained  by  making,  simply  for  my  own  use,  as  I dissected 
through  the  depth  of  a part,  a multitude  of  sketches,  which  were  placed  side  by  side 
and  carefully  examined  in  succession : the  plan  is  tedious  and  demands  patience,  brrt  can 
be  confiderrtly  recommended  to  anatomists  as  a valuable  expedient  for  ascertaining  the 
arrarrgernents  of  a complicated  arrd  intricate  structure  of  which  the  parts  are  so  con- 
tirrually  changirrg  their  course  and  relative  position,  in  var^dng  planes,  that  in  the  dissec- 
tioir  each  must  rrecessarily  be  destroyed  whilst  seekirrg  its  relation  to  others*. 
Medulla  oblongata. 
(3.)  Anatomists  are  aware  that  the  medulla  spinalis  consists  externally  of  longi- 
tudinal white  fibres,  but  internally  of  grey  substance ; and  that  the  latter  communicates 
with  the  surface  by  nieans  of  the  posterior-lateral  sulcus  which  divides  the  white  sub- 
stance of  each  lateral  half  into  a posterior  and  an  antero-lateral  column.  Through  this 
sulcus  or  fissure,  a few  of  the  roots  of  the  spinal  nerves  are  connected  with  the  central 
grey  portion,  while  the  rest  reach  it  through  the  posterior  white  columns,  to  which, 
therefore,  they  are  exclusively  attached,  as  I first  pointed  out  in  a former  communi- 
cation to  the  Royal  Society  'f*.  In  the  medulla  oblongata,  a considerable  difference  exists 
in  the  arrangement  and  relative  position  of  the  white  and  grey  columns,  and  new  struc- 
tures are  superadded.  Fig.  5,  Plate  XII.  represents  the  posterior  aspect  of  the  human 
medulla  oblongata,  and  fig.  6 a side  view  of  the  same,  enlarged.  On  each  side  of  the 
anterior  median  sulcus  is  the  corpus  pyramidale  anterius  (^?‘,  figs.  6 and  9).  Adjoining 
this,  along  its  outer  border,  we  find  the  olivary  column  [h,  fig.  6),  which  contains  or 
encloses  the  corpus  olivare,  and  is  separated  by  the  lateral  column  [g)  and  by  the  posterior 
* In  the  method  I formerly  employed,  I have  succeeded  in  maldng  very  great  improvements,  which  will 
be  explained  on  some  future  occasion. 
t Philosophical  Transactions,  1851.  Part  II. 
