The microstructure of lingual papillae in the Egyptian fruit bat (Rousettus aegyptiacus) as observed by light microscopy and scanning electron microscopy

The microstructure of lingual papillae on the dorsal surface of the tongue of adult Egyptian fruit bats was examined by light microscopy (LM) and scanning electron microscopy (SEM). This elongated tongue with a rounded apex is approximately 3 cm long -- including the 1.7cm length of the anterior free part of the tongue -- which facilitates considerable freedom of movement. The surface of the tongue has four types of lingual papillae: two types of mechanical papillae -- filiform and conical papillae, and two types of gustatory papillae -- fungiform and vallate papillae. Most numerous are filiform papillae with well developed keratinized processes represented by four morphological subtypes -- small, giant, elongated, and bifid papillae. Our observations showed the small and giant filiform papillae to be present in the anterior part of the tongue and tilted to the back of the tongue. In the posterior part of the tongue, the filiform papillae with elongated processes were arranged on each side of the tongue and oriented perpendicularly to the median line of tongue. This arrangement of filiform papillae is considered to be useful for the efficient uptake of semiliquid food as it can be collected toward the median line of the tongue. Gustatory fungiform papillae were distributed among filiform papillae on the border of the apex and the anterior part of the body of the tongue and also on the posterior part of the tongue, while three vallate papillae surrounded by conical papillae were found on the root of the tongue. There were also taste buds along the ducts of the posterior lingual glands in the posterior-lateral part of the tongue. These morphological features are discussed in relation to adaptation to food uptake in the Egyptian fruit bat.