sacculus

English Thesaurus

1. a small sac or pouch (especially the smaller chamber of the membranous labyrinth) (noun.body)

hypernym	:	sac,
definition	:	a structure resembling a bag in an animal (noun.body)

part meronym	:	membranous labyrinth,
definition	:	the sensory structures of the inner ear including the labyrinthine receptors and the cochlea; contained within the bony labyrinth (noun.body)