1. (Zoöl.) 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. Muscæ volitantes (. Etym: [L., flying flies.] (Med.) Specks or filaments apparently seen moving or glinding about in the field of ...