COMPARATIVE LIGHT AND SCANNING ELECTRON MICROSCOPIC STUDIES ON THE TONGUE OF THE NILE CROCODILE, CROCODYLUS NILOTICUS AND THE DESERT FAT SAND RAT, PSAMMOMYS OBESUS

Abstract

The dorsal lingual surface of the Nile crocodile, Crocodylus niloticus, a carnivorous freshwater reptilian animal and the desert fat sand rat, Psammomys obesus, a herbivorous mammal, were examined by the light and Scanning Electron microscopes. Filiform (Fl), fungiform (FU) and circumvallate papillae (CI) were observed in the tongue of the Nile crocodile while the sand rat tongue contained only, (Fl) and (FU) papillae. In the crocodile the fungiform papillae were scattered in clusters among the filiform ones and contained taste buds. In the fat sand rat, however, the filiform papillae were denselydistributed all over the dorsal surface of the lingual body and flowershaped (FU) papillae were scarcely found in between. Histologically, the dorsal lingual epithelium revealed differences between the two animals. In the crocodile it consisted of a stratified squamous epithelium while in the fat sand rat it consisted of a keratinized stratified squamous epithelium. Taste buds were found in the lingual epithelium of the crocodile but completely absent in that of the fat sand rat. The lingual submucosa of the crocodile contained a network of melanophores and numerous lymphocytic aggregations which werecompletely absent in that of the fat sand rat. The mucous glands were present in the ventral lingual mucosa of the fat sand rat but completely absent in that of the crocodile. The tongue of the crocodile was supported by a cartilaginous rod which was longer than that of the fat sand rat. It may be concluded that the histological differences between the tongues of both Crocodylus niloticus and Psammomys obesus, obviously reflect their carnivorous and herbivorous modes of feeding respectively.