Digastric

Origin, Insertion, Action, Innervation

Origin:
Posterior belly: Mastoid notch of the temporal bone (medial to the mastoid process)
Anterior belly: Digastric fossa on the internal surface of the mandible (near the midline of the chin)
Insertion: Both bellies attach via an intermediate tendon to the hyoid bone (through a fibrous loop)
Action:
Depression (opening) of the mandible (when the hyoid is stabilized by the infrahyoid muscles)
Elevation of the hyoid bone (during swallowing)
Stabilization of the hyoid during phonation
Innervation:
Posterior belly: Facial nerve (CN VII) — digastric branch
Anterior belly: Mylohyoid nerve — a branch of the mandibular division of the trigeminal nerve (CN V3)

Palpation Guide

Client position: Supine with the neck in neutral or slight extension.
Landmark sequence:

Posterior belly: Locate the mastoid process. The posterior belly runs from the mastoid notch (medial to the mastoid process) downward and forward toward the hyoid bone. Palpate in the space between the mastoid process and the angle of the mandible — the posterior belly runs through this area, deep to the SCM.
Anterior belly: Place your fingertip under the chin, just lateral to the midline. The anterior belly runs from the digastric fossa of the mandible downward and backward toward the hyoid. It is palpable as a small, thin muscle belly in the submental triangle.
Intermediate tendon: The two bellies meet at the hyoid bone via a fibrous loop. The hyoid is palpable in the anterior neck, at approximately C3 level, as a small horseshoe-shaped bone.

Tissue feel: Both bellies are thin and small compared to the masseter or temporalis. The posterior belly feels like a thin cord running from behind the mandibular angle toward the hyoid. The anterior belly is a small, soft muscle under the chin.
Confirmation test: Ask the client to open the jaw against resistance applied under the chin. The digastric bellies contract as accessory jaw openers. You can feel the anterior belly engage in the submental region.
Common errors:
Confusing the posterior belly with the SCM — the SCM is superficial and lateral; the posterior belly of the digastric is deep and medial, running from the mastoid notch to the hyoid.
Missing the anterior belly entirely — it is small and lies in the submental triangle under the chin, where students rarely palpate.
Confusing the hyoid bone with the thyroid cartilage — the hyoid is superior to the thyroid cartilage and is freely mobile (it can be grasped gently and moved side to side).

Trigger Point Referral

Common TrP locations: The posterior belly has TrPs near the mastoid process. The anterior belly has TrPs in the submental triangle under the chin.
Referral pattern: Posterior belly TrPs refer to the SCM region and lower teeth. Anterior belly TrPs refer to the lower front teeth (incisors) and the chin/throat area.
Clinical significance: Lower incisor pain that the dentist cannot explain may originate from anterior digastric TrPs. This is less common than masseter or temporalis referral to the teeth but should be considered when those muscles have been treated without resolution.

Trigger point referral diagram — coming soon

Image coming soon. For visual reference, see [Digastric at TriggerPoints.net](http://www.triggerpoints.net/muscle/digastric).

Clinical Notes

Innervation significance:

Unique dual innervation — the posterior belly is CN VII (facial nerve) and the anterior belly is CN V3 (trigeminal). This reflects the muscle's embryological derivation from two different pharyngeal arches. Clinically, facial nerve palsy (Bell's palsy) can weaken the posterior belly without affecting the anterior belly.

Common conditions:

Assists jaw opening and is therefore involved in conditions/tmj-dysfunction, though it is a secondary contributor compared to the lateral pterygoid.
Posterior belly hypertonicity can develop alongside SCM and suboccipital dysfunction in conditions/whiplash and chronic cervical pain presentations.
Hyoid bone stabilization dysfunction can contribute to swallowing difficulty and throat discomfort — relevant in complex TMJ and cervical presentations.

What you'll typically find:

The digastric is rarely the primary clinical finding. It is most commonly encountered as part of a broader TMJ or cervical treatment when the masseters, temporalis, and pterygoids have been addressed and residual symptoms remain.
The posterior belly is more clinically relevant than the anterior belly — it lies in the region between the mastoid process and the angle of the mandible where multiple muscles converge (SCM, posterior belly of digastric, stylohyoid).

Treatment effects:

Gentle compression of the posterior belly in the space between the mastoid process and the mandibular angle. Use minimal pressure — the area is sensitive and the facial nerve is in proximity.
Anterior belly work in the submental triangle — light fingertip compression. Clients may find this area uncomfortable due to its proximity to the throat.
Post-treatment effects are subtle compared to masseter or temporalis release. The digastric contributes to overall TMJ balance rather than producing dramatic immediate changes.

Cautions:

The facial nerve (CN VII) exits the stylomastoid foramen near the posterior belly's origin. Avoid heavy pressure at the mastoid notch.
The submandibular gland lies in the submandibular triangle, adjacent to the digastric. It feels lobulated and distinct from muscle tissue — do not compress it aggressively.
The external carotid artery and its branches are in proximity to the posterior belly. Avoid sustained deep pressure in this region.

Clinical pearl:

If a client reports difficulty swallowing or a sense of throat tightness alongside TMJ symptoms, the suprahyoid muscles (digastric, mylohyoid, stylohyoid) may be contributing by altering hyoid position. The hyoid should be freely mobile — gently grasp it and assess its lateral mobility. If it is fixed or restricted, the suprahyoid group may need attention.

Assessment

Manual muscle testing:

Jaw depression (opening): Client supine. Ask the client to open the jaw against resistance under the chin. The digastric assists the lateral pterygoid. Isolated testing of the digastric is not clinically practical.

Stretch test:

Jaw closure with hyoid depression: No standard clinical stretch test isolates the digastric. Restricted jaw opening suggests involvement of the entire jaw-opening group.

Related special orthopedic tests:

TMJ palpation during opening/closing — note jaw deviation and restricted opening
Hyoid mobility assessment — gentle lateral translation of the hyoid to assess freedom of movement

Muscle Groups

Suprahyoid muscles (anatomical):

Digastric (this article)
Mylohyoid
Stylohyoid
Geniohyoid

Jaw depressors (openers) (functional):

anatomy/muscles/lateral-pterygoid — primary opener
Digastric (this article)
Mylohyoid
Geniohyoid

Dual innervation group (innervation):

Digastric (this article) — CN VII (posterior belly), CN V3 (anterior belly)

Related Muscles

Synergists for jaw depression:

anatomy/muscles/lateral-pterygoid — primary jaw opener; the digastric is an accessory opener

Antagonists:

anatomy/muscles/masseter — primary jaw closer
anatomy/muscles/temporalis — jaw closer and retractor
anatomy/muscles/medial-pterygoid — jaw closer

Clinically related:

anatomy/muscles/sternocleidomastoid — the posterior belly of the digastric lies deep to the SCM; both are involved in cervical and TMJ presentations

Key Takeaways

A secondary jaw opener with dual innervation (CN VII posterior, CN V3 anterior) — unique embryological origin from two pharyngeal arches.
Lower incisor pain without dental pathology may be anterior digastric TrPs — consider after ruling out masseter and temporalis referral.
Assess hyoid mobility in TMJ clients with swallowing difficulty — a fixed hyoid suggests suprahyoid group involvement.