Anatomy and Structure - The digastric muscle is a bilaterally paired suprahyoid muscle located under the jaw. - It consists of two muscular bellies united by an intermediate tendon. - The posterior belly attaches to the mastoid notch of the temporal bone. - The anterior belly attaches to the digastric fossa of the mandible. - The two bellies meet at the intermediate tendon. - The tendon perforates the stylohyoideus muscle. - The tendon is embraced by a fibrous sling attached to the hyoid bone.

Innervation - The anterior belly receives motor innervation from the mylohyoid nerve, a branch of the inferior alveolar nerve. - The posterior belly is supplied by the digastric branch of the facial nerve. - The digastric muscle has dual innervation from the mandibular division of the trigeminal nerve (CN V) and the facial nerve (CN VII).

Relations - The posterior belly is situated posterior to the parotid gland and the facial nerve. - The digastric muscle divides the anterior triangle of the neck into four smaller triangles: submandibular triangle, carotid triangle, submental triangle, and inferior carotid triangle. - The digastric muscle plays a role in defining the boundaries of these neck triangles.

Variation - The intermediate tendon may be absent in some individuals. - The posterior belly may partly or entirely arise from the styloid process of the temporal bone. - The digastric muscle may have additional slips connecting it to other muscles. - The anterior belly may be double or have extra slips passing to the jaw or mylohyoideus. - The digastric muscle may fuse with the mylohyoid muscle or show variations in its attachment points.

Additional Facts - The two bellies of the digastric muscle have different embryological origins. - The mylohyoid nerve is a branch of the inferior alveolar nerve, which is a branch of the mandibular division of the trigeminal nerve (CN V).