MR.  J.  L.  CLAEKE  ON  THE  INTIMATE  STEUCTUEE  OF  THE  BEAIN. 
243 
Of  the  Corpora  Olivaria. 
(26.)  The  corpora  olimria  were  first  made  known  by  Eustachius  in  his  eighteenth 
plate,  and  were  so  named  by  Vieussens.  Although  denied  by  Eolando,  Leueet,  Longet 
and  some  others,  they  are  certainly  found  not  only  in  Mammalia,  but  even  to  a certain 
extent  in  Birds ; but  difier  somewhat  in  form.  In  Man  they  are  larger  than  in  any  of 
the  inferior  animals,  except  the  Elephant ; and  next  in  dimensions  are  those  of  the  Ape- 
tribe  and  Cetacea  (Dolphin  and  Porpoise). 
(27.)  Structure. — In  Man  each  corpus  olivare  is  separated  from  the  pons  by  a deep 
depression,  which  in  animals  is  occupied  by  a broad  band  called  the  trapezium  (see 
figs.  3,  4,  7,  9).  Its  surface  consists  of  two  layers  of  fibres,  transverse  and  longitudinal : 
the  former  belong  to  the  arciform  system,  the  latter  are  continuous  with  the  antero- 
lateral column  on  the  outer  side  of  the  pyramid.  It  is  well  known,  that  in  a transverse 
section,  the  corpus  dentatum,  or  grey  substance  of  the  olive,  appears  in  the  form  of  a 
convoluted  lamina  refiected  upon  itself  at  the  sm-face,  or  like  the  longitudinal  section 
of  a sac  placed  transversely  and  somewhat  obliquely  with  its  mouth  near  the  raphe  and 
its  fundus  at  the  surface  (see  figs.  28  etseq.,  Plate  XVI.).  In  such  a section  the  folds  of 
the  lamina  are  more  or  less  at  right  angles  to  its  course ; but  in  sections  made  longitudi- 
nally and  in  intermediate  directions  they  are  seen  to  be  prolonged  sideways,  and  to  be 
continuous  ufith  others  in  different  planes  and  at  various  angles ; so  that  the  entire  area  of 
the  sac  is  unequally  and  diversely  undulated.  Fig.  24,  Plate  XV.  represents  a longitu- 
dinal section  with  part  of  the  olivary  (white)  column.  Here  the  convolutions  are  seen  to 
bear  a striking  resemblance  to  those  of  the  cerebral  hemispheres,  for  they  are  formed  on 
the  same  plan ; and,  like  them,  the  vesicular  sac  encloses  a white  nucleus  of  fine  tubular 
fibres,  which  have  the  same  kind  of  relation  to  its  folds  as  the  central  fibres  of  the  hemi- 
spheres have  to  their  convolutions;  and  further,  it  is  joined  to  its  fellow  of  the  opposite 
.side  by  a transverse  commissure,  consisting  of  separate  bundles,  which  communicate,  how- 
ever, and  cross  the  raphe  behind  the  anterior  fissure  (figs.  30,  31,  32).  The  average 
thickness  of  the  lamina  is  about  -^oth  of  an  inch.  Its  cells  are  of  small  but  rather  uniform 
size,  and  measure  from  to  the  Twswfli  of  an  inch  in  diameter ; but  in  shape  they 
vaiy  from  the  globular  to  the  oval,  the  pyriform,  the  prismatic,  and  the  semilunar,  accord- 
ing, apparently,  to  the  number,  relative  distance  and  direction  of  their  processes:  these  are 
generally  numerous : I have  seen  as  many  as  eight  proceeding  from  one  cell : they  extend 
in  different  directions,  transverse,  longitudinal  and  oblique,  and  are  broad  at  their 
origin,  but  frequently  taper  rapidly  like  a short  spur,  or  divide  abruptly  into  several 
branches,  which  become  continuous  with  the  nerve-fibres  (see  fig.  22,  Plate  XIII.,  and 
fig.  25,  Plate  XV.).  Each  cell  encloses  a large  globular  or  elliptical  nucleus,  containing 
a very  distinct  nucleolus. 
(28.)  Behind  the  olivary  sac  is  a separate  elongated  mass  composed  of  the  same  kind 
of  cells ; and  a similar  but  larger  mass  (broken  into  parts  by  bundles  of  the  deep  arci- 
form fibres)  is  found  in  front  of  the  lamina,  near  the  side  of  the  raphe.  The  former 
2 K 2 
