1. Sinusoidal vibrations delivered to the ventral surface of the urodeles Salamandra salamandra and Triturus cristatus result in sinusoidal displacements of the fluid in the perilymph foramen.
2. The displacing force is transmitted either via the cranial cavity or via the ear capsule.
3. The displacements are of considerably greater amplitude than those of the skull at frequencies between 50 and 400 Hz.
4. These large displacements are explained in terms of a hydraulic system, based on the dimensions of structures associated with the ear.
5. This system, together with a suitably located receptor organ, the amphibian papilla, provides a vibration-detection system of potentially greater sensitivity than one relying on otolith granules.
6. The perilymph duct may act as a shunt pathway, allowing gross low-frequency displacements of the perilymph to bypass the amphibian papilla.