Underside of the tongue, artwork. At centre is the lingual frenulum, which attaches the tongue to the bottom of the mouth. To its right is the plica fimbriata, a fold in the thin epithelial surface of the tongue. At bottom left are the ends of the lingual vein (blue) and artery (red). Part of the underside of the tongue has ben sectioned to show the anterior lingual gland (top centre), which secretes mucus and serum to lubricate the tongue. The lines of striated muscle, the bulk of the tongue, can also be seen. The tongue is one of the taste organs and is also important in the formation of speech, mastication (chewing) of food and swallowing.