(2)  On  the  back  6f  the  articulation  there  are  (a)  recurrent
branches  from  the  posterior  carpal  arch,  and  (h)  from  the  first
dorsal  interosseous  artery ;  and  (c)  branches  from  the  posterior
interosseous.  The  posterior  interosseous,  or  posterior  termi-
nation of  the  anterior  interosseous,  forms  a  free  anastomosis
with  branches  from  the  radial  and  ulnar,  which  curve  round  the
respective  bones,  and  from  the  chain  thus  formed  twigs  run
along  in  the  8yno\ial  sheath  of  each  of  the  tendons,  supplying
the  sheath  and  giving  filaments  to  the  tendons.  From  these
branches  to  the  sheath  and  tendons  vessels  enter  the  back  of
the  wrist  and  carpal  joints.
(3)  Piercing  the  external  lateral  ligament,  and  thus  entering


280      MUSCLES   OF   THE   RADIO-CARPAL   ARTICULATIOK.
immediately  into   the  wrist-joint,  are  twigs  derived  from  the
radial  as  that  vessel  passes  over  the  external  lateral  ligament.
(4)  Similarly  others  enter  the  wrist  from  the  ulnar  on  the  inner
side,  while  others  penetrate  the  internal  lateral  ligament  to  reach
the  inter-articular  cartilage  and  the  inferior  radio-ulnar  joint.
The  Nerves. — In  front,  the  ulnar  and  the  median  ;  and
behind,  the  posterior  interosseous.  Each  gives  filaments  to
this  joint.
