The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a bilaterally paired suprahyoid muscle located under the

jaw The jaws are a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth ...

. Its posterior belly is attached to the mastoid notch of temporal bone, and its anterior belly is attached to the digastric fossa of mandible; the two bellies are united by an intermediate tendon which is held in a loop that attaches to the hyoid bone. The anterior belly is innervated via the mandibular nerve (cranial nerve V), and the posterior belly is innervated via the facial nerve (cranial nerve VII). It may act to depress the mandible or elevate the hyoid bone. The term "digastric muscle" refers to this specific muscle even though there are other muscles in the body to feature two bellies.

Anatomy

The digastric muscle consists of two muscular bellies united by an intermediate tendon with the posterior belly longer than the anterior belly. The two bellies of the digastric muscle have different

embryological Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, ''-logia'') is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos an ...

origins - the anterior belly is derived from the first brachial arch and the posterior belly from the second brachial arch and thus differ in their innervation.

Structure

Posterior belly

The posterior belly attaches at the mastoid notch of the temporal bone (which is located upon the inferior surface of the skull, medial to the

mastoid process The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, t ...

of the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

- between the mastoid process and the styloid process of the temporal bone). It extends antero-inferiorly from its osseous attachment toward the intermediate tendon.

Anterior belly

The anterior belly attaches at the digastric fossa of mandible (situated at the base of the mandible near the midline). It extends postero-inferiorly from its origin toward the intermediate tendon.

Intermediate tendon

The two bellies meet at the intermediate

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

which perforates the stylohyoideus muscle. The tendon is embraced by a fibrous sling which attaches the body and

greater cornu The hyoid-bone (lingual-bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid-cartilage. At rest, it lies between the base of the mandible and the third cervical verteb ...

hyoid bone The hyoid-bone (lingual-bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid-cartilage. At rest, it lies between the base of the mandible and the third cervical verte ...

. The tendon occasionally features a

synovial sheath A synovial sheath is one of the two membranes of a tendon sheath which covers a tendon. The other membrane is the outer fibrous tendon sheath. The tendon invaginates the synovial sheath from one side so that the tendon is suspended from the membra ...

Innervation

The anterior belly receives motor innervation from the

mylohyoid nerve The mylohyoid nerve (or nerve to mylohyoid) is a mixed nerve of the head. It is a branch of the inferior alveolar nerve. It provides motor innervation the mylohyoid muscle, and the anterior belly of the digastric muscle. It provides sensory inn ...

(a branch of the

inferior alveolar nerve The inferior alveolar nerve (IAN) (also the inferior dental nerve) is a sensory branch of the mandibular nerve (CN V3) (which is itself the third branch of the trigeminal nerve (CN V)). The nerve provides sensory innervation to the lower/mandibu ...

, which is in turn a branch of the mandibular division of the trigeminal nerve (CN V₃)). The posterior belly is supplied by the

digastric branch of facial nerve The digastric branch of facial nerve provides motor innervation to the posterior belly of the digastric muscle. It branches from the facial nerve (CN VII) near to the stylomastoid foramen as the CN VII exits the facial canal The facial canal ( ...

Relations

The posterior belly is situated posterior to the parotid gland while the anterior belly is closer to the sub-mandibular salivary gland which is a content of the digastric triangle.

Triangles of the neck

The digastric muscle divides the

anterior triangle of the neck The anterior triangle is a region of the neck. Structure The triangle is inverted with its apex inferior to its base which is under the chin. Investing fascia covers the roof of the triangle while visceral fascia covers the floor. Anatomy M ...

into four smaller triangles: the submandibular triangle (digastric triangle), the

carotid triangle The carotid triangle (or superior carotid triangle) is a portion of the anterior triangle of the neck. Anatomy Boundaries It is bounded: * Posteriorly by (the anterior border of) the sternocleidomastoid muscle, * Anteroinferiorly by (the sup ...

, the submental triangle (suprahyoid triangle), and the inferior carotid triangle (muscular triangle).

Variation

The intermediate tendon may be absent. The posterior belly may arise partly (by a supplemental strip of muscle) or entirely from the styloid process of the temporal bone. It may be connected by a

muscle slip Anatomical terminology is used to uniquely describe aspects of skeletal muscle, cardiac muscle, and smooth muscle such as their actions, structure, size, and location. Types There are three types of muscle tissue in the body: skeletal, smooth, a ...

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. It may be absent and posterior belly inserted into the middle of the jaw or hyoid bone. It may fuse with the

mylohyoid muscle The mylohyoid muscle or diaphragma oris is a paired muscle of the neck. It runs from the Human mandible, mandible to the hyoid bone, forming the floor of the oral cavity of the human mouth, mouth. It is named after its two attachments near the mo ...

. The tendon may pass in front, more rarely behind the stylohyoideus. The mentohyoideus muscle passes from the body of hyoid bone to chin.

Actions/movements

The muscle depresses the mandible, and may elevate the hyoid bone. It depresses the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

when the hyoid bone is held in place (by the

infrahyoid muscles The infrahyoid muscles, or strap muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. The four infrahyoid muscles are the sternohyoid, sternothyroid, thyrohyoid and omohyoid muscles. Excluding the sternot ...

Function

The digastric muscle is involved in any complex jaw action such as speaking, swallowing, chewing, and breathing. The posterior belly is particularly functionally involved in swallowing and chewing.

Other animals

The digastric muscles are present in a variety of animals, specific attachment sites may vary. For example, in the

orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...

, the posterior digastric attaches to the

rather than the hyoid.

References

External links

Frontal section
* * * {{Authority control Muscles of the head and neck Suprahyoid muscles Otorhinolaryngology Human head and neck