Summary. As reptiles are situated phylogenetically between the amphibians and the mammals, they exhibit considerable variation in the structure of their tongues. The present study, one of a series of studies on reptile tongues, aims to demonstrate the three-dimensional structure of the dorsal lingual surface of a turtle, the Japanese terrapin Clemmys japonica, and to clarify the ultrastructural features of the lingual epithelial cells. In the study lingual papillae were observed by scanning electron microscopy to be widely distributed over the dorsal surface of the tongue. Irregularly shaped (conical, columnar or angular) papillae were located in the anterior and central areas, and ridge-like ones, in the latero-posterior area. Histological examination revealed that the connective tissue penetrated into the core of the papillae, and the epithelium was of a stratified squamous and/or cuboidal type. Under the transmission electron microscope, two types of cells were identified in the intermediate layer of the apical epithelium of the lingual papilla: one type was probably an immature mucous cell, whereas the other was elongated in a baso-apical direction, its cytoplasm containing fine granules. In the surface layer of the apical epithelium, typical mucous cells and cells containing numerous, fine, electron-lucent granules were recognized. Both types of cells possessed microvilli on their free-surfaces. In the lateral epithelium of the lingual papillae, the cytological features from the basal layer to the superficial intermediate layer were essentially the same as in the apical epithelium. However, in the surface layer, mucous cells were significantly larger in number than in the apical epithelium.In mammals, the tongue functions mainly for feeding (THEXTON, 1980) and for lapping (HIIEMAE et al., 1981). In some mammals, it also functions for the brushing of body hair. The relatively strong keratinization, especially of the dorsal epithelium, is associated with the performance of these functions. The keratinized epithelium forms compactly distributed fine processes or filiform papillae (FARBMAN, 1966(FARBMAN, , 1970CANE and SPEARMAN, 1969; HUME and POTTEN, 1976;BOSHELL et al., 1982;STEFLIK et al., 1983; MACKENZIE and BICKENBACH, 1984;IWASAKI andMIYATA, 1989, 1990; IWASAKI,1990a). In mammals, the tongue plays only a small part in the secretion of salivary fluid, as the major salivary glands develop to assume this purpose. By contrast, in amphibians, the tongue plays a very important role in the secretion of salivary fluid into the oral cavity, as well as in feeding (ZYLBERBERG, 1977; IWASAKI and WANICHANON,1991).Reptiles are situated phylogenetically between the amphibians and the mammals. There have been many macroscopic and light-microscopic studies on the tongues of reptiles (GNANAMUTHU, 1937;GOIN and GOIN, 1962;SMITH, 1984 SMITH, , 1986 SMITH, , 1988SCHWENK, 1986). The results of such studies have demonstrated considerable variation in the morphology and histology of the reptilial tongue. However, very few rep...
