Digastric muscle

Origin: Anterior belly - digastric fossa (mandible); posterior belly - mastoid process of temporal bone

Insertion: Intermediate tendon (hyoid bone)

Nerve: Anterior belly - mandibular division of the trigeminal(CN V) via the mylohyoid nerve; posterior belly -facial nerve (CN VII)

Action: Opens the jaw when the masseter and the temporalis are relaxed.

Description:
The Digastricus (Digastric muscle) consists of two fleshy bellies united by an intermediate rounded tendon. It lies below the body of the mandible, and extends, in a curved form, from the mastoid process to the symphysis menti. The posterior belly, longer than the anterior, arises from the mastoid notch of the temporal bone and passes downward and forward. The anterior belly arises from a depression on the inner side of the lower border of the mandible, close to the symphysis, and passes downward and backward. The two bellies end in an intermediate tendon which perforates the Stylohyoideus muscle, and is held in connection with the side of the body and the greater cornu of the hyoid bone by a fibrous loop, which is sometimes lined by a mucous sheath. A broad aponeurotic layer is given off from the tendon of the Digastricus on either side, to be attached to the body and greater cornu of the hyoid bone; this is termed the suprahyoid aponeurosis.