The tongue occupies the floor of the oral cavity. It is divided into an anterior two-thirds (the oral part) and a posterior third (the pharyngeal part) by a prominent sulcus terminalis.

The oral part has a velvety appearance, being covered by small projections called papillae. Most of these are pointed filiform papillae, with numerous mushroom-shaped and taste bud-containing fungiform papillae interspersed among them.

The pharyngeal part lies posterior to a row of very large taste bud-containing circumvallate papillae just anterior to the sulcus terminalis. The posterior third of the tongue is nodular from underlying masses of lymphoid tissue, the lingual tonsils.

Tongue muscles

Muscles of the tongue muscles are divided into intrinsic and extrinsic. The intrinsic muscles change the shape of the tongue and are arranged as longitudinal, transverse, and vertical fibres. The extrinsic muscles move the tongue:

• Genioglossus attaches to the anterior part of the mandible, and pulls the tongue forwards (protrusion).
• Hyoglossus attaches to the hyoid bone, and pulls the tongue down and posteriorly (retraction and depression).
• Styloglossus attaches to the styloid process, and retracts and elevates the tongue.
• Palatoglossus attaches to the palate and depresses the palate more than it elevates the tongue.

Nerve supply to tongue

All tongue muscles are supplied by the hypoglossal nerve (CN XII), except palatoglossus supplied by the pharyngeal plexus of the vagus nerve (CN X). The anterior two-thirds is supplied by the lingual nerve for general sensation and the chorda tympani for taste. The posterior third is supplied by the glossopharyngeal nerve. Sensation to a small part above the epiglottis is supplied by the internal laryngeal branch of the vagus nerve.

CLINICAL CORNER

Hypoglossal nerve damage may be caused by tumours, penetrating injuries and various neurological conditions. The tongue may show wasting and fasciculations (spontaneous quivering movements caused by nerve misfiring). Unopposed action of genioglossus of the unaffected side will lead to deviation of the tongue towards the damaged side.