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

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.

Innervation

The anterior belly receives motor innervation from the mylohyoid nerve (a branch of the inferior alveolar nerve, 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.

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

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