The digastric muscle (also digastricus or musculus biventer mandibulae) (named digastric as it has two 'bellies') is a bilaterally paired suprahyoid muscle located under the jaw. Its posterior belly is attached to the mastoid notch of temporal bone, and its anterior belly is attached to the digastric fossa of mandible; the two bellies are united by an intermediate tendon which is held in a loop that attaches to the hyoid bone. The anterior belly is innervated via the mandibular nerve (cranial nerve V), and the posterior belly is innervated via the facial nerve (cranial nerve VII). It may act to depress the mandible or elevate the hyoid bone.
The term "digastric muscle" refers to this specific muscle even though there are other muscles in the body to feature two bellies.
Anatomy
The digastric muscle consists of two muscular bellies united by an intermediate tendon with the posterior belly longer than the anterior belly. The two bellies of the digastric muscle have different embryological origins - the anterior belly is derived from the first brachial arch and the posterior belly from the second brachial arch and thus differ in their innervation.
Structure
Posterior belly
The posterior belly attaches at the mastoid notch of the temporal bone
It extends antero-inferiorly from its osseous attachment toward the intermediate tendon.
thumb|right|300px|Anterior view of digastric muscle
Relations
The posterior belly is situated posterior to the parotid gland while the anterior belly is closer to the sub-mandibular salivary gland which is a content of the digastric triangle.
Triangles of the neck
The digastric muscle divides the anterior triangle of the neck into four smaller triangles: the submandibular triangle (digastric triangle), the carotid triangle, the submental triangle (suprahyoid triangle), and the inferior carotid triangle (muscular triangle).
Variation
The intermediate tendon may be absent. The posterior belly may arise partly (by a supplemental strip of muscle) or entirely from the styloid process of the temporal bone.