Lower jaw (mandible)

The mandible is the only movable cranial bone. It is a single bone connected to the skull at both temporomandibular joints. Like the maxilla, it is also a part of the viscerocranium of the skull. The mandible forms the lower jaw, and it presents with three parts:

 

 

Body of mandible

The body of the mandible is the anterior central part of the lower jawbone. It has a curved shape and can be subdivided into two smaller portions: 

The body of the mandible has two surfaces (external and internal) and two borders (superior or alveolar and inferior).

 

 

Base of mandible

The base of the mandible the inferior, thickened part of the body, and it has external and internal surfaces.

The features on the external surface of the mandibular base are:

The landmarks found on the internal surface of the mandibular base include the following:

 

 

Alveolar process of mandible

The alveolar process of the mandible is the superior crested portion of the body of the mandible. It surrounds and supports the lower teeth

Its curved free margin is called the alveolar arch. The alveolar arch of the mandible (like the alveolar arch formed by the maxillae) features the following landmarks:

 

 

Ramus of mandible

The rami of the mandible are situated on the right and left side of the mandible. They extend upward from the body of the mandible. Each ramus of the mandible features several landmarks:

Like the body of the mandible, the ramus also has internal and external surfaces.

The internal surface of the ramus features the following landmarks:

  • Mandibular foramen - an opening leading into the mandibular canal that serves as a bony passage for the inferior alveolar artery, inferior alveolar vein and inferior alveolar nerve;
  • Lingula - a triangular-shaped bony ridge extending superior from the mandibular foramen;  it is also known as the Spix's spine; 
  • Mylohyoid groove - a groove on the internal surface of the mandible extending forward and downward from the mandibular foramen; it transmits the mylohyoid nerve (a branch of the inferior alveolar nerve) and the mylohyoid branch of the inferior alveolar artery (from the maxillary artery);
  • Pterygoid tuberosity - a roughened area present on the internal surface of the mandibular ramus near the angle of the mandible; it serves as the attachment site for the medial pterygoid muscle.

The external surface of the mandibular ramus presents the masseteric tuberosity - a roughened area present near the angle of the mandible. This tuberosity is the attachment site for the masseter muscle.