It has papillae of different shapes: filiform papillae for feeling and foliate, fungiform, and vallate papillae for perceiving taste stimuli. The mucous membrane of the dorsum is thick and partly cornified. The frenulum linguae, a fold of mucous membrane, descends from the middle of the tongue’s underside to the floor of the mouth. The underside of the tongue is covered by a thin mucous membrane salivary ducts open between the folds of the membrane and near the root of the tongue. On the dorsum, between the body and the root, is situated the foramen cecum linguae, which is an atretic thyroid duct. The mammalian tongue consists of the free part (or body), the apex, and the root (by which the tongue is attached to the lower jaw and hyoid bone). In humans the tongue has also become an organ of speech. In edentates and some ungulates the tongue is used to grasp food. In mammals the tongue is capable of particularly free movement because of its complex musculature and reduction of the hyoid bone. The shape of the avian tongue is extremely varied and is related to the diet of the particular species. Parrots have a broad, fleshy, movable tongue. The tongue is covered by cornified epithelium. It usually is incapable of free movement, although it can be thrust forward in woodpeckers and hummingbirds. In birds the tongue is also connected to the hyoid bone. The tongue of snakes and some lizards is bifurcated at the front and moves quickly it is used to feel and analyze chemically (for taste) surrounding objects. The long tongue of chameleons is covered with a sticky substance that aids in catching insects. The tongue of crocodiles and turtles moves only inside the mouth. In reptiles the anterior portion of the sublingual skeleton, the hyoid bone, lies at the base of the tongue. This feature is unknown in all other vertebrates. In some amphibians the posterior end of the tongue is free the tongue is ejected to catch insects, tipping downward with the free back edge. Most tailless amphibians use the tongue to catch prey. The tongue is able to move independently and serves to grasp food, move the food within the mouth, and swallow the food. All terrestrial vertebrates develop tongue musculature, derived from the sublingual parietal musculature. In amphibians numerous mucous glands are found on the dorsum, that is, the superior surface of the tongue. In fishes the tongue is a fold of the mucous membrane it has no muscles (except in dipnoans) and moves with the entire visceral skeleton when the sublingual-branchial apparatus moves. The unpaired growth on the floor of the mouth in humans and other vertebrates.
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