Digastric muscle

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Digastric muscle
Digastricus.png
Muscles of the neck. Lateral view.
Gray1195.png
Front view of neck.
Latin musculus digastricus
Gray's p.391
Origin anterior belly - digastric fossa (mandible); posterior belly - mastoid process of temporal bone
Insertion Intermediate tendon (hyoid bone)
Artery anterior belly - Submental branch of facial artery; posterior belly - occipital artery
Nerve anterior belly - mandibular division (V3) of the trigeminal (CN V) via the mylohyoid nerve; posterior belly - facial nerve (CN VII)
Actions Opens the jaw when the masseter and the temporalis are relaxed.
Anatomical terms of muscle

The digastric muscle (also digastricus) (named digastric as it has two bellies) is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bellies include the ligament of treitz, omohyoid, occipitofrontalis.

It lies below the body of the mandible, and extends, in a curved form, from the mastoid process to the symphysis menti. It belongs to the suprahyoid muscles group.

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.

Structure[edit]

The digastricus (digastric muscle) consists of two muscular bellies united by an intermediate rounded tendon.

The two bellies of the digastric muscle have different embryological origins, and are supplied by different cranial nerves.

Posterior belly[edit]

The posterior belly, longer than the anterior belly, arises from the mastoid notch which is on the inferior surface of the skull, medial to the mastoid process of the temporal bone. The mastoid notch is a deep groove between the mastoid process and the styloid process. The mastoid notch is also referred to as the digastric groove or the digastric notch.

The posterior belly is supplied by the digastric branch of facial nerve.

The digastric muscle stretches between the mastoid process of the cranium to the mandible at the chin, and part-way between, it becomes a tendon which passes through a tendinous pulley attached to the hyoid bone. It originates from the second pharyngeal arch.

Anterior belly[edit]

The anterior belly arises from a depression on the inner side of the lower border of the mandible called the Digastric Fossa, close to the symphysis, and passes downward and backward.

The anterior body is supplied by the trigeminal via the mylohyoid nerve, a branch of the inferior alveolar nerve, itself a branch of the mandibular division of the trigeminal nerve. It originates from the first pharyngeal arch.

Intermediate tendon[edit]

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.

Action[edit]

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).

Variations[edit]

Variations are numerous.

The posterior belly may arise partly or entirely from the styloid process, or be connected by a 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 Stylohoideus. The Mentohyoideus muscle passes from the body of hyoid bone to chin.

Anterior view of digastric muscle

Other animals[edit]

The digastric muscles are present in a variety of animals, specific attachment sites may vary. For example, in the Orangutan, the posterior digastric attaches to the mandible rather than the hyoid.

Triangles[edit]

The Digastricus divides the anterior triangle of the neck into three smaller triangles.

  • (1) the submandibular triangle(also called 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

Additional images[edit]

External links[edit]

This article incorporates text from a public domain edition of Gray's Anatomy.