all fours \all` fours"\ formerly, all` four".
   all four legs of a quadruped; or the two legs and two arms of
   a person.
   1913 webster

   to be, go, or run, on all fours fig., to be on the
      same footing; to correspond with exactly; to be alike in
      all the circumstances to be considered. "this example is
      on all fours with the other." "no simile can go on all
      fours." --macaulay.
      1913 webster
see also:
all` four" to be go run on all fours