Digastric muscle

Hello again! It’s Matt from Kenhub, and in this tutorial, we will be discussing the digastric muscle. The digastric muscle is one of the suprahyoid muscles. This group consists of four muscles running from the mandible to the hyoid bone. Together with adjacent tissue, they form the floor of the mouth.

The digastric muscle consists of two parts which are separated by an intermediate tendon. They are the anterior belly and the posterior belly. One particular feature of the digastric is that both bellies have different embryological origins.

The anterior belly of the digastric muscle, which this part of the muscle I am pointing to here, originates from the digastric fossa of mandible and inserts together with the posterior belly on the intermediate tendon. The anterior belly is derived from the first pharyngeal arch and is therefore innervated by a branch of the mandibular nerve called the mylohyoid nerve.

The posterior belly of the digastric muscle is this part of the muscle seen here. The posterior belly is longer than the anterior belly and originates from the mastoid notch of temporal bone on the medial side of the mastoid process. It has its insertion on the intermediate tendon together with the anterior belly. In contrast to the anterior belly, the posterior belly arises from the second pharyngeal arch which is why its nerve supply comes from the facial nerve.

From below, the mouth floor is reinforced by the anterior bellies of the digastric muscles. The suprahyoid muscles do not only form the floor of the mouth but play an important role in chewing, swallowing and speech. In combination with the infrahyoid muscles, they are responsible for the positioning of the hyoid bone. In particular, the anterior belly of the digastric muscle acts to pull the mandible forward and depress it whereas the posterior belly draws back the hyoid bone.

All in all, due to their contribution during mastication, the suprahyoid muscles are also referred to as accessory muscles of mastication. The digastric muscle also divides the anterior triangle of the neck into three smaller divisions: submandibular triangle, carotid triangle, submental triangle.

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