Fine structure of the fungiform papilla in a ranid frog (Rana esculenta).

The freetop of the fungiform papilla shows a sensorial area about 100 micron in diameter, surrounded by a ring of ciliated cells. Externally to the ciliated cells, i.e., in the lateral wall, numerous large goblet cells can be seen devoid of their mucous content. The sensorial area is composed by three types of cells: mucous, supporting, and neuroepithelial cells. Mucous cells form the most superficial layer, while the cell bodies of the other two are deep, and from them basal and apical processes arise. The above mentioned cells are connected by desmosomes preferentially located between the mucous and the supporting cells, rather than between the supporting and the neuroepithelial cells. The lateral wall of the papilla is made up of a multilayered epithelium that comprises two types of cells: the first type contains electron-dense granules and an abundant rough endoplasmic reticulum, the others are ciliated cells. In the connective axis of the papilla, numerous fenestrated capillaries with endothelial vesiculated cells and nerve fibers are found.