Fine structure of the dorsal lingual epithelium of the frog, Rana rugosa

Scanning and transmission electron microscopy was employed to investigate the ultrastructure of the lingual dorsal epithelial cells of the frog, Rana rugosa. The specimens for scanning electron microscopy were prepared by a method that involved osmium postfixation and treatment with acid to remove extracellular material that adhered to the surface of the tongue. Over almost the entire dorsal surface, filiform papillae, consisting of a large number of non-ciliated cells with microridges and a very small number of ciliated cells, were compactly distributed. Fungiform papillae were scattered among these filiform papillae. A round sensory disk was located on the top of each fungiform papilla. Each sensory disk was encircled by a band of ciliated cells. Transmission electron microscopy revealed that a large part of the filiform papillar epithelium was composed of cells that contained numerous electron-dense granules. These cells were coincident with the non-ciliated cells observed by scanning electron microscopy. In these cells, the nucleus was located on the basal side, and the ergastoplasm was well-developed on the basal side of the nucleus.