ME.  J.  L.  CLAEKE  ON  THE  INTIMATE  STEUCTUEE  OF  THE  BEAIN. 
235 
whole  of  the  medulla  on  each  side,  and  to  be  developed  in  a remarkable  degree.  In 
bu'ds,  reptiles  and  fishes  they  may  be  seen  without  difficulty. 
Of  the  Corpora  Pyramidalia  Anteriora. 
(8.)  External  appearance. — The  anterior  pyramidal  columns  were  first  pointed  out 
in  the  plates  of  Eustachius  towards  the  end  of  the  sixteenth  century,  and  were  so  named 
by  Willis,  who  considered  them  as  the  channels  by  which  the  animal  spirits  were  con- 
veyed from  the  cerebellum  to  the  par  vagum  and  contiguous  nerves^.  In  Man,  as  is 
well  known,  they  are  largely  developed,  and  appear  at  the  lower  border  of  the  pons  as 
two  thick  and  rounded  cords,  which  flatten  as  they  descend  to  meet  each  other  at  a 
point.  They  are  also  of  considerable  but  variable  size  in  all  the  Mammalia,  and  in  some 
of  the  larger  beasts  of  prey,  as  the  Lion,  Hyoena  and  Jaguar,  I have  found  their  exter- 
nal dimensions  to  be  nearly,  if  not  quite,  equal  to  those  of  Man ; but  in  depth  they  are 
mostly  smaller  among  this  class  of  animals.  Well  marked,  prominent  and  rounded  in 
the  Quadrumana, — at  least  in  the  Shniadce, — they  are  broad  and  fiat,  but  usually  longer 
in  the  Herhivora ; and  in  the  Elephant,  although  far  from  proportionally  broad  in  rela- 
tion to  the  size  of  the  brain,  they  are  long  and  tapering.  “ Dans  I’hypothese,”  says 
Seeres,  “ que  les  pyramides  sont  les  racines  des  lobes  cerebraux,  leur  developpement 
de'VTait  etre  en  raison  directe  de  ceux-ci ; or  c’est  ce  qui  n’est  pas ; les  pyramides  sont 
moins  fortes  chez  I’homme  que  chez  les  singes ; elles  sont  plus  prononcees  aussi  chez  les 
cetacees.  Cette  predominence  des  pyramides  se  continue  chez  les  carnassiers,  le  lion, 
I’oui’s,  le  raton,  la  loutre ; chez  les  pachydermes  et  les  ruminansf .”  In  relation  to  the 
size  of  the  cerelrum,  it  is  true  that  the  anterior  pyramids  are  smaller  in  Man  than  in 
some  of  these  animals,  particularly  the  larger  Carnivora,  as  the  Lion  and  Hyaena ; but 
actually  their  dimensions  are  in  most  instances  much  greater.  In  the  Herhivora  espe- 
cially, the  supeiUcial  breadth  of  the  pyramids  is  no  indication  of  their  actual  bulk,  which 
can  be  ascertained  only  by  means  of  transverse  sections ; for  although  they  are  frequently 
very  broad,  and  rendered  prominent  at  one  part  by  the  olivary  bodies  behind  them,  they 
are  much  more  shallow  than  in  Man,  and  their  decussating  fibres  are  much  less  nume- 
rous, as  will  be  shown  at  a future  pagej. 
(9.)  Structure. — Perhaps  no  question  in  anatomy  has  been  the  subject  of  greater 
dispute  than  that  which  concerns  the  decussation  of  the  anterior  pyramids.  The  oppo- 
nents have  been  nearly  equal  in  number  and  celebrity,  and  the  confidence  with  which 
they  have  maintained  their  opinions  has  rendered  the  case  somewhat  remarkable  §. 
* Cerebri  Anatome,  cap.  .3  (1664).  f Anatoinie  Comparee  du  Cerveau,  tom.  ii.  p.  187. 
X I must  acknowledge  the  readiness  and  kindness  with  which  Mr.  Quekett  and  Mr.  Mueie,  of  the 
Eoyal  College  of  Surgeons,  assisted  me  in  procuring  the  brains  of  many  of  these  animals. 
§ For  instance,  Saxtoeixi,  speaking  of  the  decussation,  observes,  “Nos  autem  sic  earn  luculenter  con- 
speximus,  sic  evidenter,  ubi  apta  incidere  cadavera  demonstravimus,  ut  nulla  amplius  nobis  de  hac  re  super- 
sit dubitandi  ratio”  (Observationes  Anatomicse,  cap.  iii.  1724).  On  the  other  hand,  the  illustrious  and 
laborious  Hallee,  after  describing  the  anterior  median  sulcus,  continues,  “ Hanc  rimam  si  diduxeris,  fibrse 
quasi  medullares  adparent,  quee  a dextra  columna  meduUse  oblongatfe  in  sinistram  transeimt,  trausversEe 
2 I 2 
