Digastric muscle

How is the digastric muscle structured?

The muscle consists of two parts connected by an intermediate tendon:

• Anterior belly (venter anterior) — originates from the digastric fossa of the mandible (fossa digastrica). The second layer of the cervical fascia forms sheaths for the anterior bellies of the m. digastricus.
• Posterior belly (venter posterior) — originates from the mastoid notch of the temporal bone (incisura mastoidea).
• Intermediate tendon — connects both muscle bellies and attaches to the body of the hyoid bone via a fibrous loop (via fibrous loop).

What is its function?

The action of the muscle depends on which bony structure is fixed:

• Depression of the mandible: when the hyoid bone is fixed, the muscle depresses the mandible.
• Elevation of the hyoid bone: when the mandible is fixed, the muscle elevates the hyoid bone.

During mouth opening, the mandibular condyles first rotate, then glide downward and forward along the slope of the articular tubercle. At maximum opening, the distance between the cutting edges of the upper and lower incisors averages 4–5 cm.

Blood supply and innervation

Due to the differences between the muscle bellies, they are innervated from different sources:

• Innervation of the anterior belly: mylohyoid nerve (n. mylohyoideus), originating from the trigeminal nerve (n. trigeminus).
• Innervation of the posterior belly: facial nerve (n. facialis).
• Blood supply: submental artery (a. submentalis) and occipital artery (a. occipitalis).

Topography and adjacent structures

The bellies of the m. digastricus participate in forming the boundaries of cervical regions and triangles:

• Submandibular region (trigonum submandibulare): bounded anteriorly and posteriorly by the anterior and posterior bellies of the digastric muscle, respectively. The region contains the submandibular salivary gland, facial vessels (a. et v. facialis), and lymph nodes.
• Submental triangle (trigonum submentale): located between the anterior bellies of the right and left digastric muscles. The cellular tissue of the triangle contains 1–2 submental lymph nodes, which drain lymph from the tip of the tongue, the middle part of the floor of the oral cavity, and the middle part of the lower lip.
• Jugulodigastric lymph node (nodus lymphoideus jugulodigastricus): palpable at the angle of the mandible and located at the level of intersection of the internal jugular vein (v. jugularis interna) and the digastric muscle.

Clinical significance

Knowledge of the topography of the digastric muscle is important when evaluating neck masses:

• Lateral (branchial cleft) cervical cysts: the upper pole is often located near or beneath the posterior margin of the m. digastricus.
• Dermoid and epidermoid cysts of the neck: may be localized between the posterior belly of the digastric muscle and the anterior margin of the sternocleidomastoid muscle.

Class and exam questions

What else to study on this topic

• Submandibular triangle of the neck
• Submental triangle of the neck
• Biomechanics of mandibular movements
• Cervical fascia and fascial spaces

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.