Digastric muscle: anatomy of the submental region
- Muscle
- Nerve
- Highlighted area
Quick facts
- Anterior belly
- Arises from the digastric fossa, on the inner surface of the mandible near the midline, and runs down to the intermediate tendon.
- Posterior belly
- Arises from the mastoid notch of the temporal bone, behind the ear, and runs down to the intermediate tendon.
- Intermediate tendon
- Held to the hyoid bone by a fibrous sling.
- Innervation
- Anterior belly by the mylohyoid nerve (branch of the trigeminal); posterior belly by a branch of the facial nerve.
- Function
- Lowers the mandible when opening the mouth and raises the hyoid bone in swallowing.
- Relevance in facial harmonization
- The anterior belly can contribute to central submental volume that is not fat.
The digastric is a neck muscle made of two bellies, anterior and posterior, joined by an intermediate tendon held to the hyoid bone. The anterior belly runs from the inner surface of the chin to the hyoid, in the submental region; the posterior belly runs from the area behind the ear to the same point. It lowers the mandible and raises the hyoid, and in facial harmonization it matters because the anterior belly can make up part of the volume under the chin that is mistaken for a double chin.
Where is it and how is it organized?
| Part | Origin and course | Innervation |
|---|---|---|
| Anterior belly | Digastric fossa, on the inner surface of the mandible near the midline, running down and back to the tendon | Mylohyoid nerve, a branch of the mandibular nerve (trigeminal) |
| Intermediate tendon | Passes beside the hyoid bone, held to it by a fibrous sling | Not applicable |
| Posterior belly | Mastoid notch of the temporal bone, running down and forward to the tendon | Digastric branch of the facial nerve |
The double innervation reflects the different embryonic origin of each belly. The two anterior bellies, one on each side, bound the submental triangle together with the hyoid. Each anterior belly, with the posterior belly and the border of the mandible, bounds the submandibular triangle, where the submandibular gland sits.
What are the layers of the submental region?
From the skin inward, the area under the chin has skin, subcutaneous fat, platysma, subplatysmal fat, the anterior bellies of the digastric and, beneath them, the mylohyoid muscle, which forms the floor of the mouth. Each layer contributes in a different way to the volume seen in profile.
Why does it matter in facial harmonization?
- Submental volume that is not fat: bulky anterior bellies form a central bulge under the chin, sometimes as two columns. This volume does not respond to fat treatments.
- Cervicomental angle: the digastric, together with the position of the hyoid, helps define the cervicomental angle. A low, anterior hyoid leaves the angle more open, which an injectable does not correct.
- Expectations in double chin treatment: separating subcutaneous fat, subplatysmal fat, muscle and gland avoids indicating the wrong procedure. The sequence is in double chin: assessment.
How does it show up in the assessment?
- Profile with the head in the Frankfurt plane: shows the contour under the chin without distortion from posture.
- Pinch test: subcutaneous fat can be pinched; muscular volume lies below the platysma and cannot be pinched.
- Swallowing and mouth opening: the anterior belly becomes firmer when it contracts.
- Ultrasound: helps separate fat, muscle and gland when in doubt.
Also called: digastric, digastric muscle of the mandible, anterior belly of the digastric.
Frequently asked questions
Can the digastric muscle cause a double chin?
It can contribute. In some people, the anterior bellies of the digastric are bulky or become more visible with age and form a bulge under the chin. Because it is muscle, this volume does not decrease with treatments aimed at fat.