The afferent and efferent nerve endings of the outer hair cells of the rabbit and the guinea pig were investigated electron-microscopically. The rabbit: In the afferent nerve endings, the partially thick and dense membranes on either side of the synaptic cleft were observed. In the efferent nerve endings, synaptic vesicles were concentrated at some sites opposite the synaptic cleft and in some places of the synaptic cleft there were gaps (0.16-0.68μm) which contained small vesicles. The findings of the afferent and efferent nerve endings of the guinea pig were the same as that of the rabbit.
