The tongue is also called as the lingua or glossa. It is a highly muscular organ used for lapping water, prehension (grasping) of food, manipulating the food within the mouth and swallowing. It also possesses receptors for taste, temperature and pain.
It is covered with stratified squamous epithelium. In the anterior part, it forms specialized structures known as papillae. Based on their function they are grouped as mechanic papillae and gustatory papillae. Mechanic papillae are cornified and aid in licking while protecting the deeper layers. The gustatory papillae are covered with taste buds. Mechanical papillae are more numerous than gustatory ones.
The skeletal muscle of the tongue runs in three different directions. This allows for a wide range of movements needed to properly manipulate foodstuffs. The types, numbers and distribution of papillae in the tongue vary greatly among species.
In domestic animals there are usually five different types of papillae.
1) Filiform papillae are highly keratinized and sharply pointed. They aid in mechanically
breaking up food material. They are numerous in ruminants and cats where they are used in
lapping milk. They are the smallest and most numerous of all papillae.
2) Fungiform papillae are smooth with a rounded surface. They help manipulate the food
but also have taste buds on their lateral surfaces.
3) Conical papillae are somewhat larger than fungiform papillae. They are used in manipulating
and breaking down ingested food. They can be distinguished from fungiform papillae by
their larger size and their tendency to project above other papillae. They do not have taste buds.
4) Foliate papillae are covered with non-keratinized stratified squamous epithelium. They are leaf-shaped
structures defined by an invagination of the mucous membrane on their sides. Many
taste buds on their lateral surfaces indicate their role in gustation. They are absent in
ruminants but well developed in the horse and dog.
5) Circumvallate papillae are the largest (up to 1/8 inch diameter) papillae. They are
surrounded by a deep indentation of the mucous membrane and are not numerous. They do
not rise above the surface of the tongue. Many taste buds are located on their sides. Serous
von Ebner's glands empty into the "moat" around these papillae and help keep it free of food