sacculus

n. saccule, small baglike structure in a plant or animal

Located within the vestibular system of the inner ear, the saccule is one of the otoliths which gathers sensory information to orient the body. The saccule primarily gathers sensory information about linear movement in the vertical plane. The saccule, or sacculus, is the smaller of the two vestibular sacs; it is globular in form, and lies in the recessus sphæricus near the opening of the scala vestibuli of the cochlea.
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Noun
1. a small sac or pouch (especially the smaller chamber of the membranous labyrinth)
(synonym) saccule
(hypernym) sac
(part-holonym) membranous labyrinth

(n.)
A little sac; esp., a part of the membranous labyrinth of the ear.
  

a satchel; a hood.