Investigations were performed by light microscope on the surface area of the ampulla of the semicircular canal in the guinea pig. Besides the conventional sections, dissected specimens of the ampulla after silver reaction (silver nitrate staining) were used. The surface view of the sensory epithelium of the crista ampullaris was shown by this method. The sensory epithelium of the crista ampullaris was encircled with cylindrical prismatic cells, which made a gradual transition with the supporting cells of the sensory epithelium on one side, but made an abrupt transition with the dark cell area on both the utricular and canalicular sides and formed the plana semilunata on both lateral sides of the ampulla. The free surface of each planum semilunatum cell was smaller near the sensory epithelium becoming larger towards the roof of the ampulla. The roof cells of the ampulla which were continuous with the planum semilunatum cells without any specific border, became smaller towards the midline at the top of the ampullary dome. This midline of smaller cell area extended in both utricular and canalicular directions.