The Fine Structure and Elemental Analysis of Keratinized Epithelium of the Filiform Papillae Analysis on the Dorsal Tongue in the American Alligator (Alligator mississippiensis)

Abstract

The filiform papillae of subadult alligator (120 cm-260 cm total length) tongues are examined by scanning electron microscopy and electron microprobe analysis. The filiform papillae form cone-like structures and are observed over the entire dorsal surface of a relatively long tongue with a round tip. The filiform papillae are composed of four layers; outer, upper intermediate, lower intermediate, and basal layer. The keratinized epithelial cells are analysed by the sulphur (S), and nitrogen (N) content levels. The S content is higher than that of N. In the anterior side of the filiform papillae, this content is lower than that in the posteriors. The S content is highest of all at about 2 microns in depth from the surface. These results suggest that the use of S concentration measurements may serve to be an effective tool for a simple, offhand evaluation of keratinization.

Studies on Tongue of Reptilian Species Psammophis sibilans, Tarentola annularis and Crocodylus niloticus

“…Shimada et al (1990) reported that the dorsum tongue of the A. mississippiensis is covered with small, evenly distributed cone-shaped filiform papillae spread across the dorsal surface of the tongue. The small, nipple-like surface projections seen in the Nile crocodile probably represent the papillae observed in the American alligator.…”

Fine structure of the dorsal lingual epithelium in Tarentola annularis and Crocodylus niloticus

“…The more discrete surface units occupying the caudal regions of the tongue were characterised by the presence of numerous flattened, disc-shaped structures at the centre of which there was a small pore. The small, nipple-like surface projections seen by SEM in the present species C. niloticus probably represent the papillae observed in the American alligator [38,45].…”

“…The most interesting features of the histological structures of reptilian tongues reflect adaptations to a dry habitat or to seawater, but stratification and keratinisation of the lingual epithelium are common features [19,20]. The alligator is an aquatic reptile and its lingual epithelium is strongly keratinised [19,45]. In the present study, T. annularis and C. niloticus, the epithelium were typically keratinised stratified squamous in structure but in C. niloticus the keratinisation appeared thin and uniform in thickness throughout all regions of the tongue except for thickenings containing taste buds and highly folded zone.…”

“…Shimada et al [45] reported that the dorsal surface of the tongue of A. mississippiensis is covered with palate during mastication and swallowing. It provides tongue with a rough surface suited for the movement and grinding of food [25,33,54].…”

“…The results of such studies have demonstrated considerable variety in the morphology and histology of the reptilian tongue. It should be stated that, only a few microscopic and ultrastructural observation of the lingual epithelium of crocodile have been reported [2,11,26,45]. The tongue of Crocodylia has been discussed in variety of publications, mainly in regard to the presence of lingual glands and their participation in salt secretion [47,53].…”