Tongue of vertebrate shows much diversity and are not homologous. Tongue is gustatory organ. It is a soft muscular organ situated on the floor of the buccal cavity. The mucous membrane below the tongue forms a median fold called frenulum which joins tongue to the floor of the mouth.
|MORPHOLOGY OF TONGUE|
Tongue is divided into two regions:
1. Papillar area: anterior 2/3 of the tongue where lingual papillae are present.
2. Lymphoid area: posterior 1/3 of the tongue which lacks lingual papillae but is lymphoidal.
The dorsal surface of the papillar area shows a median groove called median succus or lingual septum.
Tongue in section reveals following details:
|SLIDE VIEW OF TONGUE|
Tongue is composed of intercalary bundles of striped muscle fibers which are embedded in a bedding substance called lamina propria, made up of areolar tissue. Also present in areolar tissue are blood vessels, nerves and glands of von ebner.
The muscle fibers are disposed in three directions: oblique, transverse and longitudinal.
The entire tongue is covered by mucous membrane lined by squamous epithelium.
Along the ventral surface of the mucous membrane is smooth but along the dorsal surface it is thrown into a number of projections called lingual papillae.
There are four types of lingual papillae:
i. Circumvallate papillae: lie on the base of the tongue they have taste buds at its base. They are large but few in numbers, each are surrounded by a groove.
|SLIDE VIEW OF CIRCUMVALLATE PAPILLAE|
ii. Fungiform papillae: are second largest but more in number than circumvallate papillae. They are distributed all over the surface of the tongue. Each Fungiform papillae show a narrow basal end and a club shaped free end that projects above the surface prominently. The papillae appear red in colour as they have rich blood supply. Secondary papillae are also present.
iii. Filiform papillae: are smallest but numerous of all types of papillae. They are distributed all over the tongue. Each papilla has a conical elevation directed posteriorly. It is covered by cornified epithelium that is produced into thread like strands.
iv. Foliate papilla: are broad and leaf like lying hear the base of the tongue in parallel rows and are sharp in nature. They bear taste buds on their sides. Usually these are found at the tip of the tongue. In cows it is more common. In human it is absent.