The base is the lowest, thickened part of the body of the mandible. Each of its surfaces features different landmarks described below. In craniometry, the midpoint on the lower border of the body is known as the gnathion.

Anatomical landmarks of external surface

The external surface of the mandibular base has the following landmarks:

Mental protuberance - a triangular-shaped eminence at the midline of the body that forms the chin;
Mental tubercle - small bony prominence on each side of the mental protuberance;
Mental foramen - a large opening located usually below the second mandibular premolar; it transmits the mental vessels and nerve; sometimes there are multiple foramina instead of one opening;
Oblique line - a weak bony crest that extends into the body from the root of the ramus; it usually ends posterior to the mental foramen.

Note: The mental foramen is an important landmark, as it allows access to the mental nerve for local anesthesia. The mental nerve is a branch of the inferior alveolar nerve, which arises from the mandibular nerve (CN V3).

Anatomical landmarks of internal surface

The features found on the internal surface of the mandibular base are as follows:

Superior mental spine and inferior mental spine - two small paired bony elevations in the midline of the internal surface that project towards the tongue; they are found on the lower aspect of the surface; they serve as the attachment sites for the genioglossus muscle and geniohyoid muscle ;
Digastric fossa - an oval depression found in the lower part of the internal surface; it is found below and lateral to the mental spines; this fossa serves as the attachment site for the anterior belly of the digastric muscle;
Mylohyoid groove - an oblique groove that extends from the posterosuperior aspect of the ramus and body to the anteroinferior aspect of the body;
Mylohyoid line - an oblique crest found above the mylohyoid groove; it begins just inferior to the third mandibular molar and goes in the anteroinferior direction; it serves as an origin site for the mylohyoid muscle; its posterior part is also the origin of the superior pharyngeal constrictor muscle;
Submandibular fossa - a paired depression located below the middle part of the mylohyoid line; it houses the submandibular gland;
Sublingual fossa - a paired depression found in the premolar region above the medial end of the mylohyoid line; it houses the sublingual gland.

Note: Sometimes, the mandible can have a bony, non-tender outgrowth on the inner surface of the body called the mandibular torus. It is usually found in the canine or premolar region above the attachment of the mylohyoid muscle.

Unlock with Premium

Lower jaw (base of mandible)