Fig.  20. — Position  of  the  hand  in  long-standing  paralysis  and  wasting  of  the  thenar  muscles.    Under  the

influence  of  the  long  extensor  the  metacarpal  bone  of  the  thumb  has  been  brought  into  the  same  position

as  the  other  metacarpal  bones,  being  rotated  slightly,  so  that  the  back  of  the  thumb  is  in  the  plane  of

the  back  of  the  hand,  like  the  hand  of  the  ape.    (After  Duchenne.)
Fig.  21,  from  another  case,  shows  the  same  condition,  but  still  greater  displacement  of  the  metacarpal

bone  has  taken  place,  from  the  greater  contraction  of  the  extensor.     (After  Duchenne.')

metacarpal  bone  inward  and  backward.  The  whole  thumb  corresponds  with  the  meta-
carpal bone  in  position,  the  phalanges  being  normal.  In  paralysis  of  the  short  abductor
and  flexor,  the  second  phalanx  cannot  be  extended  unless  the  metacarpal  bone  is  ab-
ducted. These  short  muscles  normally  prevent  the  ab-
duction that  the  extensor  of  the  second  phalanx  tends  to
produce.  The  latter,  moreover,  prevents  undue  adduc-
tion when  the  special  abductors  are  paralyzed,  but  brings
the  metacarpal  bone  into  the  plane  of  the  index.  Thus
the  posture  of  the  hand  at  rest  resembles  that  of  the  hand
of  an  ape  (Figs.  19  and  20).  If  the  abductor  and  oppo-
nens  are  paralyzed,  the  tips  of  the  thumb  and  fingers  can
only  be  brought  together  by  flexing  the  last  phalanges  of
the  digits  (Fig.  22).  Then  the  thumb  can  be  brought
into  contact  with  the  finger  by  means  of  the  short  flexor,
which  inclines  the  metacarpal  bone  sufficiently  to  effect
this,  although  not  enough  for  the  tip  of  the  first  finger  to
touch  the  thumb  when  its  phalanges  are  extended.
