The Digastric has two bellies
(anterior and posterior) united by a single tendon attached to the hyoid bone.
The posterior belly attaches to the mastoid groove. The anterior belly attaches
to the mandible. The facial nerve and the nerve to mylohyoid innervate the posterior
and anterior bellies, respectively.
The digastric depresses and retracts the chin, and assists the lateral pterygoid in opening the mouth.