Source : Webster's Revised Unabridged Dictionary (1913)

Perilymph \Per"i*lymph\, n. (Anat.)
   The fluid which surrounds the membranous labyrinth of the
   internal ear, and separates it from the walls of the chambers
   in which the labyrinth lies.

Source : WordNet®

perilymph
     n : the bodily fluid that fills the space between the bony
         labyrinth and the membranous labyrinth of the inner ear