Whole membranous labyrinths of the bull frogs were used in order to replicate the human vestibule.The posterior semicircular canals (PSC) were exposed leaving the remaining membranous labyrinth encapsulated in the otic capsule. The membranous labyrinth was cut by 0.5 mm at the crus commune to create a tiny opening. The cupula was visualized by gently injecting India ink of the opening. The motion of the cupula was analyzed during compression of the canal wall by a needle. The motion appeared to be that of a "diaphragma" when the compression was weak. The motion appeared to be that of a "swing door" with the base of the cupula hinged on the crista when the compression was strong.
A small piece of otoconia removed from the sacculus of the other ear was introduced through this opening into the canal lumen. The position of the preparation was controlled so that the otoconia were attached onto the cupular surface. This was regarded as a cupulolithiasis model. We performed the same experiments on the cupulolithiasis models and results were almost same, except that the motion of the cupula of cupulolithiasis models was shorter than those of the normal models. It was inferred that the motion of the cupula of cupulolithiasis models was suppressed by the weight of the otoconia.
It was observed that the india ink traversed the cupula during the compression and even the otoconia traversed the cupula. Therefore, it was inferred that the adhesion of the cupula and the ampula wall is not strong, thus protecting the cupula from detaching from the crista.
