236 
ME.  J.  L,  CLAEKE  ON  THE  INTBIATE  STEECTrEE  OE  THE  BEATN'. 
The  decussation  was  first  asserted  by  Domexico  Mistichelli  in  1709*.  It  was  con- 
firmed and  more  clearly  pointed  out  the  following  year  by  the  excellent  Poeefoue  du 
Petit  f;  and  has  since  been  described  by  Saxtoeixi,  Eachetti,  Wixslow,  Lieutaed, 
ScAEPA,  Gall,  Duveexey,  Scemmeeixg,  Valextix,  Beedach,  TiEDEiiAXX,  Eosexthal, 
Ceuveilhiee,  Seeees,  Eeid,  Foville,  Solly,  Kollikee.  On  the  other  band,  it  has  been 
denied  by  Hallee,  Moegagxi,  Boyee,  Sabatiee,  Chaessiee,  Peochasea.,  Vicq  D’Azye, 
Dumas,  Bichat,  Eolando,  Muxeo,  Desmoulixs,  and  more  recently  by  StillixgJ.  At 
the  present  day  the  balance  of  opinion  is  decidedly  in  favour  of  a decussation,  although 
the  late  microscopical  researches  of  Stillixg  may  have  added  some  weight  to  the  oppo- 
site side§.  I am  prepared,  however,  to  place  the  fact  beyond  all  possibility  of  doubt; 
for  a cursory  inspection  of  my  preparations  is  sufficient  to  show  that  a complete  and 
complicated  decussation  actually  takes  place.  But  still  the  real  composition  and  ele- 
mentary structure  of  the  pyramids,  as  I shall  now  proceed  to  show,  has  not  hitherto 
been  accurately  described. 
(10.)  Until  the  commencement  of  the  present  century,  it  was  beheved  by  those  who 
admitted  the  fact  in  question,  that  the  anterior  pyramids  are  formed  by  a decussation 
between  the  anterior  columns  of  the  spinal  chord.  Eosexthal  ||  corrected  this  error  by 
pointing  out  the  important  fact  that  the  fibres  of  decussation  proceed  from  the  lateral 
columns ; but  at  the  same  time  he  thought  that  from  the  latter  the  whole  of  the  ppu- 
mids  are  formed  as  new  or  separate  structures  by  running  along  the  fissure  bet^'een 
the  anterior  columns,  which  they  thrust  aside  in  their  course.  Such  is  stiU  the  general 
opinion,  but  such  is  not  the  correct  one,  as  I shall  endeavour’  shortly  to  explain. 
(11.)  At  the  lower  extremity  of  the  human  medulla  oblongata  (figs.  10  and  11,  Plates 
XII.  and  XIII.),  the  ggosterior  and  lateral  white  columns  are  broader  and  deeper,  but  the 
anterior  (I)  are  in  every  way  less  than  in  the  dorsal  or  lumbar  region.  The  central  canal 
is  entirely  closed  by  a mass  of  granular  matter,  and  is  much  nearer  the  bottom  of  the 
quidem,  quas  nunquain,  cum  s£epe  inquisivissem,  vidi  decussari,  aut  ad  obliques  se  secure  augulos.” — Elemeuta 
Physiologise,  lib.  x.  tom.  iv.  p.  80. 
* Trattato  dell’  Apopplesia,  cap.  iv.  p.  13.  As  the  work  is  uncommon,  and  I have  not  seen  the  passage 
that  is  referred  to  anywhere  quoted,  I here  subjoin  the  principal  portion.  “ Arrivati  all’intorno,  e ultimo 
velame  si  e osservato,  che  tutto  quel  caudice  al  di  fuori  si  pub  assomigliare  ad  una  treccia  di  Donna, 
posciache  inolti  manipoli  di  fibre  rette  sono  sovraposti  a molti  trasversali,  molti  obliqui  alii  trasversali,  et  alii 
retti,  e seguitando  questo  intrecciamento  ciascun  ordine  ritorno  a sovraporsi,  e sottoporsi,  sinche  le  dette 
fibre  escano  dalla  treccia  trasversalmente  per  formare  li  nervi  spinali,  che  sono  ne  i lati.” 
t Lettres  d’un  Medecin  des  Hopitaux  du  Eoi.  Namur,  4to.  p.  12 ; accompanied  with  figures,  which  are 
very  far  superior  to  those  of  Mistichelli. 
X TJeber  die  Medulla  Oblongata. 
§ “ A crossing  of  the  pyramid- fibres  is  nowhere  to  be  perceived,”  he  says,  “ Eine  Kreuzung  der  Pp’aiui- 
denfasern  ist  nirgends  walirzunehmen.”  He  attributes  such  an  appearance  to  the  unsymmeti’ical  manner 
in  which  the  alternate  bundles  on  each  side  meet  and  indigitate  (TJeber  die  Medulla  Oblongata,  p.  29). 
He  also  describes  these  bundles  of  fibres  as  arising  from  the  anterior  commissure  at  the  bottom  of  the 
fissure,  p.  27. 
II  Bin  Beitrag  zur  Encephalotomie.  8vo.  Weimar,  1815. 
