Digastric muscle

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 bia 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. The digastric muscle consists of two muscular bellies united an intermediate tendon. The posterior belly is longer than the anterior belly. The two bellies of the digastric muscle have different embryological origins - the anterior belly is derived from the first brachial arch and the posterior belly from the second brachial arch - and consequently differ in their innervation (the former being innervated via CN V and the latter via CN VII). 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 - between the mastoid process and the styloid process of the temporal bone). It extends anteroinferiorly from its osseous attachment toward the intermediate tendon. The anterior belly attaches at the digastric fossa of mandible (situated at the base of the mandible near the midline). It extends inferoposteriorly from its origin toward the intermediate tendon. The two bellies meet at the intermediate tendon which perforates the stylohyoideus muscle. The tendon is embraced by a fibrous sling which attaches the body and greater cornu of hyoid bone. The tendon occasionally features a synovial sheath.

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