The digastric is a two-bellied suprahyoid muscle with different embryological origins and nerve supplies for each belly. The posterior belly (branchial arch 2 origin — facial nerve) is used as a landmark during neck dissection — the posterior digastric belly marks the posterior limit of the submandibular triangle and the position of the facial nerve as it exits the parotid. The anterior belly is used for digastric flap reconstruction.
| Origin | Anterior belly: digastric fossa of the mandible (inner surface near the symphysis). Posterior belly: mastoid notch (medial to the mastoid process) |
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| Insertion | Intermediate tendon attached to the hyoid bone via a fibrous loop — the central tendon connects the two bellies |
| Nerve Supply | Anterior belly: mylohyoid nerve (branch of the inferior alveolar nerve, V3). Posterior belly: facial nerve (VII) — the only non-facial muscle supplied by the facial nerve |
| Blood Supply | Anterior belly: submental artery. Posterior belly: posterior auricular and occipital arteries |
| Actions | Depresses the mandible (jaw opening) when the hyoid is fixed by the infrahyoid muscles; Elevates and fixes the hyoid during swallowing (with the other suprahyoids) |
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The posterior digastric belly is the key surgical landmark in neck dissection and parotidectomy: the facial nerve exits the stylomastoid foramen immediately deep and medial to the posterior digastric origin. The sternocleidomastoid, posterior digastric, and stylohyoid form the boundaries identifying the nerve trunk. The digastric's intermediate tendon is fixed to the hyoid, limiting its contraction amplitude.
The anterior belly of the digastric is palpable beneath the chin in the submental triangle during resisted jaw opening. The posterior belly is deep to the sternocleidomastoid and not palpable from the surface.
Posterior digastric belly used as the primary surgical landmark for locating the facial nerve at the stylomastoid foramen during parotidectomy.
