Posterior belly of digastric muscle

At a glance

English

Posterior belly of digastric muscle

Latin (TA2)

Venter posterior musculi digastrici

System

Muscle

Region

Neck

Side

Paired, left and right

About the posterior belly of digastric muscle

The digastric muscle under the jaw has two fleshy bellies joined by a rounded intermediate tendon. The posterior belly is the longer of the two. It starts high up behind the angle of the jaw and slopes forwards and downwards towards the hyoid bone, lying just deep to the mastoid process and parotid gland and above the internal jugular vein and carotid arteries. It is a suprahyoid muscle and a key landmark in the upper neck.

It arises from the mastoid notch, a deep groove on the underside of the skull just medial to the mastoid process, between it and the styloid process. The belly runs forwards and down, close beside stylohyoid, to become the intermediate tendon. This tendon pierces stylohyoid and is held to the hyoid body and greater horn by a fibrous loop, which turns the muscle's pull. A broad sheet of fascia, the suprahyoid aponeurosis, also spreads from the tendon to the hyoid.

The posterior belly develops from the second pharyngeal arch, so it is supplied not by the trigeminal like the front belly but by the digastric branch of the facial nerve, which leaves the facial nerve just after it exits the stylomastoid foramen. Its blood comes from the posterior auricular and occipital arteries. With the anterior belly it raises the hyoid in swallowing and speech, and it can pull the hyoid backwards; when the hyoid is fixed from below, the whole muscle helps open the mouth.

Surgeons use this belly as a guide: the facial nerve trunk, the internal jugular vein, the external and internal carotid arteries and the hypoglossal nerve all lie close to its deep surface or lower border. It forms the lower back edge of the submandibular triangle and the upper edge of the carotid triangle. It may arise partly from the styloid process, send a slip to the pharyngeal constrictors, or in rare cases end directly on the mandible or hyoid when the anterior belly is absent.

Attachments, action and supply

Origin

Mastoid notch of the temporal bone, medial to the mastoid process.

Insertion

Intermediate tendon, held to the body and greater horn of the hyoid by a fibrous loop.

Action

Raises and draws back the hyoid; with the anterior belly helps open the mouth when the hyoid is fixed.

Nerve supply

Digastric branch of the facial nerve (CN VII).

Blood supply

Posterior auricular and occipital arteries.