Ultrastructure of the Otoliths and Otolithic Membrane of the Macula Utriculi in the Guinea PIG

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Abstract
The fine structure of the otoliths and oto-lithic membrane of the macula utriculi in the guinea pig has been studied. It has been confirmed that it adopts a wavy arrangement, being formed of two zones of different electronic densiiy, one marginal and the other medial. Of these zones the former is composed of fibres and an interfibrillar substance. The latter possesses only fibres in very lax networks, which reach up to the epithelium thus demonstrating that no subcupular space exists. The otoliths are situated in the marginal zone and the sensory hair bundles in the medial. Occasionally, it is possible to find an otolith in the medial zone. However, a direct contact between otoliths and sensory hair bundles has never been observed. The otoliths measure between 6 and 20 μ ml;m in length. The body of the otolith possesses two areas of different electronic density. The peripheral is dense and the central is lighter. The extremities of the otolith consist largely of filamentous material oriented perpendicular to its facet.