Bone conduction stimulation of the teeth of the lower jaw initiates auditory sensations. However the lower jaw is only loosely coupled to the skull by the temporo-mandibular joint. Therefore the 'classical' bone conduction pathway involving skull vibration transmission entirely along bone to the temporal-petrous bone requires further consideration. Bone conduction hearing thresholds to stimulation at the forehead and at the teeth of the upper and lower jaw were determined in human subjects. Thresholds on the teeth were better than those on the forehead and there was no difference between the thresholds measured following stimulation of the upper and lower teeth. Experiments in guinea-pigs provided evidence that vibration of the teeth leads to transmission of the audio-frequency vibrations by means of soft tissue, through skull foramina, into the skull cavity (brain and CSF) and from there by fluid channels directly into inner ear fluids, exciting the cochlea.