Source : Webster's Revised Unabridged Dictionary (1913)

Musca \Mus"ca\, n.; pl. {Musc[ae]}. [L., a fly.]
   1. (Zo["o]l.) A genus of dipterous insects, including the
      common house fly, and numerous allied species.

   Note: Formerly, a large part of the Diptera were included
         under the genus {Musca}.

   2. (Astron.) A small constellation situated between the
      Southern Cross and the Pole.

   {Musc[ae] volitantes}. [L., flying flies.] (Med.) Specks or
      filaments apparently seen moving or glinding about in the
      field of vision. Their appearance is often a symptom of
      disease of the eye, or of disorder of the nervous system.

Source : WordNet®

muscae volitantes
     n : spots before the eyes caused by opaque cell fragments in the
         vitreous humor and lens [syn: {musca volitans}, {floater},
          {spots}]