The tonsils and dorsum of the tongue.
The tongue is a mobile organ which lies in the floor of the mouth. It consists of a mass of muscle covered with mucous membrane and interspaced with a small amount of fat and some glands. It is closely associated with the functions of taste, chewing, swallowing, and speaking.
It has the form of a shoe turned upside down. The opening of the shoe corresponds with the root of the tongue; through it there pass the muscles which connect the tongue with the hyoid bone and the mandible.
Besides the root, the tongue has a tip, margins, lower surface and dorsum. The tip and margins lie against the teeth and the gums. The lower surface is related to the floor of the mouth. The dorsum is divided into two parts – palatine and pharyngeal – by a V-shaped groove called the sulcus terminalis; the limbs of the V diverge widely; the apex points backwards and is marked by a pit called the foramen caecum. The palatine part of the dorsum looks upwards, and is the part visible in the living mouth. The pharyngeal part is the back of the tongue; it forms the anterior wall of the lower part of the oral pharynx, and is related to the epiglottis.
Mucous membrane of the tongue
The mucous membrane is continuous with the general lining of the mouth and pharynx, but presents very different appearances on different areas of the tongue.
On the lower surface of the tongue, the mucous membrane is smooth and comparatively thin; in the median plane, it is raised up to form the frenulum linguae. On each side of the median line, the deep lingual vein may be noticed, in the living subject, extending backwards from the tip. To the lateral side of the vein there is a delicate ridge of mucous membrane from the free border of which a row of fringe-like processes or fimbriae project. It is termed the fimbriated fold; as it extends forwards it inclines towards the median plane.
On the side of the tongue, immediately in front of the lingual attachment of the palatoglossal arch, five short vertical folds in the mucous membrane may be noticed. These are the folia linguae and they are liberally furnished with microscopic tastebuds.
The mucous membrane of the pharyngeal part of the dorsum is smooth and glossy, but it is studded with low elevations produced by masses of lymph follicles embedded in the submucous tissue; and in each elevation there is usually a small central pit. As the mucous membrane passes from the tongue to the epiglottis, it is raised into a small median glossoepiglottic fold.
The mucous membrane of the palatine part of the dorsum is studded with papillae of different kinds. As these are individually visible to the naked eye, the mucous membrane presents a very characteristic roughened appearance. Further, a shallow median groove extends from the tip of the tongue to the foramen caecum, and divides the palatine part of the dorsum into halves.