The Collaborative International Dictionary of English v.0.48:

Ventriculus \Ven*tric"u*lus\, n.; pl. Ventriculi. [L., belly,
   dim. fr. venter belly.] (Zool.)
   (a) One of the stomachs of certain insects.
   (b) The body cavity of a sponge.
       [1913 Webster]

WordNet (r) 3.0 (2006):

ventriculus
    n 1: thick-walled muscular pouch below the crop in many birds
         and reptiles for grinding food [syn: gizzard,
         ventriculus, gastric mill]