Morphological variations of the vallate papillae in some mammalian species.

The morpho-structural characteristics of the vallate papillae of the tongue of rat, dog, donkey and buffalo were investigated by macroscopy and their microstructure by light and scanning electron microscopy (SEM). The numbers of vallate papillae varied among the different species. In rat, a single vallate papilla surrounded by incomplete groove and an annular fold was observed. Taste buds were detected along the entire length of the medial and lateral groove epithelium, but not in the papillary dome. In dog, some papillae lacking the annular pad had irregular ridges and grooves toward the center of the papillary surface, while other papillae had small secondary papillary grooves arising from the center of the papilla. Taste buds were located in the medial and lateral epithelium of both primary and secondary grooves as well as in the dome epithelium. In donkey, two papillae were frequently observed around the midline of the tongue root, and an additional papilla was found occasionally in the middle and associated with secondary papilla. In buffalo, several papillae were relatively small and variable in shape. With SEM, small ridges and grooves were found in the papillae of donkey and buffalo. In both species, taste buds were constantly observed along the medial wall epithelium, but no taste buds were found in the lateral wall. We conclude that the vallate papillae exhibited peculiar characteristics, which are species specific and might have a correlation with the variable feeding habits among these animals.