The saccule of the membranous labyrinth (or simply saccule, latin: sacculus) is a part of the balancing apparatus of the inner ear lying within the vestibule. The receptors within the saccule respond to movements in the vertical plane.
The saccule is an elongated, globular-shaped membranous sac connected to the utricle and the endolymphatic duct by the utriculosaccular duct and to the cochlea by the ductus reuniens. The saccule lies within the spherical recess on the medial wall of the vestibule. It contains sensory epithelium - the macula, which is composed of hair cells and associated supporting cells.
The macula of the saccule is an oval thickening of the saccule, which lies in a vertical plane on the wall of the saccule and is formed by sensory epithelium containing receptor hair cells. Because of its vertical orientation the saccule is mainly sensitive to linear acceleration of the head in the vertical plane. The saccule serves as a gravitational sensor when the head is in an upright position and also is sensitive to movement along the anteroposterior axis.