[Show abstract][Hide abstract] ABSTRACT: Studies of the comparative morphology of the tongues of living vertebrates have revealed how variations in the morphology and function of the organ might be related to evolutional events. The tongue, which plays a very important role in food intake by vertebrates, exhibits significant morphological variations that appear to represent adaptation to the current environmental conditions of each respective habitat. This review examines the fundamental importance of morphology in the evolution of the vertebrate tongue, focusing on the origin of the tongue and on the relationship between morphology and environmental conditions. Tongues of various extant vertebrates, including those of amphibians, reptiles, birds and mammals, were analysed in terms of gross anatomy and microanatomy by light microscopy and by scanning and transmission electron microscopy. Comparisons of tongue morphology revealed a relationship between changes in the appearance of the tongue and changes in habitat, from a freshwater environment to a terrestrial environment, as well as a relationship between the extent of keratinization of the lingual epithelium and the transition from a moist or wet environment to a dry environment. The lingual epithelium of amphibians is devoid of keratinization while that of reptilians is keratinized to different extents. Reptiles live in a variety of habitats, from seawater to regions of high temperature and very high or very low humidity. Keratinization of the lingual epithelium is considered to have been acquired concomitantly with the evolution of amniotes. The variations in the extent of keratinization of the lingual epithelium, which is observed between various amniotes, appear to be secondary, reflecting the environmental conditions of different species.
Journal of Anatomy 08/2002; 201(1):1-13. DOI:10.1046/j.1469-7580.2002.00073.x · 2.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We observed the three-dimensional structures of the external surface and connective tissue cores CTCs, after exfoliation of the epithelium of the lingual papillae (filiform, fungiform, and foliate papillae) of the common hippopotamus (Hippopotamus amphibius amphibius) using scanning electron microscopy and conventional light microscopy. Following unique features were found; typical vallate papillae with a circumferential furrow were not observable. Instead, numerous large fungiform papillae were rather densely distributed on the posterior of the lingual prominence. Taste buds were observable only on the dorsal epithelium. Serous lingual gland was not seen in the lamina propria; however, mucous-rich mixed lingual glands were found and in a few of orifices were seen on the large fungiform tops. Lingual prominence was diminished their width. Rather long and slender conical papillae were distributed on the lingual prominence and were similar to nonruminant herbivore, that is donkey. Beside this narrow lingual prominence, lateral slopes were situated with numerous short spine-like protrusions. After removal of the epithelium, CTCs of lateral slopes exhibited attenuated flower bud structures. Large-conical papillae were situated on the root of the tongue. These large conical papillae were not seen among ruminants and seen on the lingual root of omnivores and carnivores. It implies that lingual structure of common hippopotamus possessed mixed characteristics between Perissodactyls, Ruminantia, and nonherbivores such as Suiformes because of their unique evolutionally taxonomic position. Moreover, adaptation for soft grass diet and associating easier mastication may be also affecting these mixed morphological features of the tongue.
The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 07/2009; 292(7):921-34. DOI:10.1002/ar.20915 · 1.53 Impact Factor
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