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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.
These four muscles have different actions, but in general assist in elevating the hyoid bone and widening the esophagus during swallowing.When the two bellies of the digastric contract, they pull upward on the hyoid bone; but if the hyoid is fixed from below, the digastric assists in extreme opening of the mouth such as yawning or taking a large bite of an apple. [1]
The four classical muscles of mastication elevate the mandible (closing the jaw) and move it forward/backward and laterally, facilitating biting and chewing. Other muscles are responsible for opening the jaw, namely the geniohyoid , mylohyoid , and digastric muscles (the lateral pterygoid may play a role).
The mastoid process serves for the attachment of the sternocleidomastoid, the posterior belly of the digastric muscle, splenius capitis, and longissimus capitis. On the medial side of the process is a deep groove, the mastoid notch, for the attachment of the digastric muscle ; medial to this is a shallow furrow, the occipital groove , which ...
The mylohyoid muscle is flat and triangular, and is situated immediately superior to the anterior belly of the digastric muscle. It is a pharyngeal muscle (derived from the first pharyngeal arch) and classified as one of the suprahyoid muscles. Together, the paired mylohyoid muscles form a muscular floor for the oral cavity of the mouth. [2]
The stylohyoid is a slender muscle. [2] It is directed inferoanteriorly from its origin towards its insertion. [3] It is perforated near its insertion by the intermediate tendon of the digastric muscle. [3]
It provides motor innervation the mylohyoid muscle, and the anterior belly of the digastric muscle. It provides sensory innervation to part of the submental area, and sometimes also the mandibular (lower) molar teeth, requiring local anaesthesia for some oral procedures.
Although it is mostly in the neck and can be grouped with the neck muscles by location, it can be considered a muscle of facial expression due to its common nerve supply. The stylohyoid muscle, stapedius and posterior belly of the digastric muscle are also supplied by the facial nerve, but are not considered muscles of facial expression.