itself a branch of the mandibular division of the trigeminal nerve. It originates from the first pharyngeal arch. Intermediate tendon 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. Variations Variations are numerous. The posterior belly may arise partly or entirely from the styloid process, or be connected by a muscle slip to the middle or inferior constrictor; the anterior belly may be double, or extra slips from this belly may pass to the jaw or mylohyoideus or decussate with a similar slip on opposite side; anterior belly may be absent and posterior belly inserted into the middle of the jaw or hyoid bone. The tendon may pass in front, more rarely behind the stylohyoideus. The mentohyoideus muscle passes from the body of hyoid bone to chin. Triangles The digastric muscle divides the anterior triangle of the neck into three smaller triangles. (1) the submandibular triangle (also called the digastric triangle), bounded above by the lower border of the body of the mandible, and a line drawn from its angle to the sternocleidomastoideus, below by the posterior belly of the digastricus and the stylohyoideus, in front by the anterior belly of the diagastricus; (2) the carotid triangle, bounded above by the posterior belly of the digastricus and stylohyoideus, behind by the sternocleidomastoideus, below by the omohyoideus; (3) the suprahyoid or submental triangle, bounded laterally by the anterior belly of the digastricus, medially by the middle line of the neck from the hyoid bone to the symphysis menti, and inferiorly by the body of the hyoid bone. (4) The inferior carotid triangle (or muscular triangle), is bounded, in front, by the median line of the neck from the hyoid bone to the sternum; behind, by the anterior margin of the sternocleidomastoideus; above, by the superior belly of the omohyoideus Function The digastric muscle is involved in any complex jaw action such as speaking, swallowing, chewing and breathing. When the digastric muscle contracts, it acts to elevate the hyoid bone. If the hyoid is being held in place (by the infrahyoid muscles), it will tend to depress the mandible (open the mouth). Other animals The digastric muscles are present in a variety of animals, specific attachment sites