190.  Cat?emaus  plexus, — ^The  superior  cervical  ganglion  of  the
sympathetic  sends  up  with  the  carotid  artery  two  or  more  slender
filaments^  which  form  a  plexus  round  it  in  its  tortuous  course
through  the  petrous  hone,  and  hy  the  side  of  the  sphenoid.  After
a  careful  dissection  we  may  discover  with  the  naked  eye  in  this
plexus  very  small  ganglia  called  carotid  or  cavernous :  hut  they
vary  in  numher,  size,  and  situation.  Through  these  nerves  a
communication  is  estahlished  hetween  the  sympathetic  and  many
of  the  nerves  which  enter  the  orhit.
Presuming  that  the  houy  framework  of  the  orhit  and  the  several
openings  in  it  he  thoroughly  understood,  we  propoi*e  to  examine
its  contents,  in  the  order  in  which  they  appear,  commencing  from
the  roof  of  the  cavity.
DISSECTION  OF  THE  ORBIT.
191.  The  roof  of  the  orhit  should  he  taken  off  by  two  vertical  cuts
made  with  a  fine  saw  ;  the  one  commencing  a  little  on  the  outer
side  of  the  internal  angular  process  of  the  frontal  hone,  in  order  to
avoid  injuring  the  beautiful  little  pulley  there  attached  ;  the  other
a  little  on  the  inner  side  of  the  external  angular  process.  With
a  hone  forceps,  the  thin  roof  of  the  oibit  should  then  be  removed
as  far  back  as  the  optic  foramen ;  and  it  is  easy  to  do  this  without
injuring  the  orbital  periosteum,  on  account  of  its  loose  coimexion
with  the  bone.
