When  the  hemispheres  are  cut  away  to  the  level  of  this  sur-
face, and  the  corpus  callosum  is  examined,  two  raised  lines
appear  in  the  middle,  which  extend  from  one  end  of  it  to  the
other  ;  and  between  them  is  a  small  groove  of  the  same  length.
This  groove  is  called  the  raphe,  or  suture  of  the  corpus  callo-
sum. From  the  raised  lines  or  bands  on  each  side  of  the  raphe,
small  lines  less  elevated  pass  across  the  corpus  callosum,  and
are  lost  in  the  medullary  matter.  The  hemispheres  being  thus
cut  off  at  the  level  of  the  corpus  callosum,  on  the  cut  surface  is
to  be  seen  the  interior  mass  of  medullary  matter,  with  the  cor-
tical part  exterior,  its  edge  exhibiting  the  convoluted  surface  of
the  brain,  and  the  pia  mater,  following  the  convolutions.
The  medullary  surface,  thus  exhibited,  with  the  corpus  cal-
losum in  the  centre,  is  denominated  the  centrum  ovale.
The  Ventricles.
In  the  brain  there  are  four  cavities  called  ventricles  :  three
of  these  are  formed  in  the  substance  of  the  cerebrum  :  the
fourth  is  situated  between  the  cerebellum,  the  pons  Varolii,
and  medulla  oblongata.  The  two  largest  are  called  the  lateral
ventricles,  from  their  situations  ;  the  others  are  named,  from
the  order  in  which  they  occur,  the  third  and  the  fourth  ven-
tricles.
