Fine structure of the tongue and lingual papillae of the penguin.

The tongue in four species of penguin was investigated by light microscopy and by scanning electron microscopy, with special reference to the lingual papillae. 1) The middle of the penguin tongue contains a pair of long cartilages and long tendons accompanied by striated muscle bundles. 2) Large, spine-like, and caudally directed lingual papillae (filiform-like papillae) densely cover the dorsal surface of the tongue, apparently serving to catch fishes. 3) By light microscopy, the dorsal lingual epithelium with the lingual papillae are seen as a thick cornified layer, but the lateral and lower surfaces have a thinner cornified layer. 4) The connective tissue core (CTC) under the epithelium of the lingual papilla shows a stereo structure similar to but smaller than the external form of the papilla. The CTC contains some blood vessels and nerve fibers; the lingual glands are found in the submucous layer only in the posterior tongue. 5) Bundles of nerve fibers in the lamina propria of the tongue were immunohistochemically positive for PGP 9.5, and it appeared that Merkel corpuscles were distributed in the connective tissue closely beneath the epithelium of the finger-like papillae, though they were only weakly immunoreactive for PGP 9.5. 6) Numerous fine filaments of elastic fibers are found closely beneath the epithelial cell layer of the dorsal surface of the tongue including the lingual papillae, while there are very few of them on the lateral and lower sides of the tongue.