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The depressor anguli oris arises from the lateral surface of the mandible. [1] Its fibers then converge. It is inserted by a narrow fasciculus into the angle of the mouth. [1] At its origin, it is continuous with the platysma muscle, and at its insertion with the orbicularis oris muscle and risorius muscle.
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 medial pterygoid muscle has functions including elevating the mandible (closing the mouth), protruding the mandible, mastication (especially for when the maxillary teeth and the mandibular teeth are close together), [1] and excursing the mandible (contralateral excursion occurs with unilateral contraction).
The primary function of the lateral pterygoid muscle is to pull the head of the condyle out of the mandibular fossa along the articular eminence to protrude the mandible. [2] A concerted effort of the lateral pterygoid muscles helps in lowering the mandible and opening the jaw.
head, nose (left/right) incisive fossa of maxilla: nasal septum and back part of alar part of nasalis: superior labial artery: facial nerve [CNVII], buccal branch: depresses nasal septum: 2 1 levator nasolabialis (levator labii superioris alaeque nasi) head, nose (left/right) frontal process of maxilla: nostril and upper lip: superior labial artery
The mylohyoid muscle elevates the hyoid bone and the tongue. This is particularly important during swallowing and speaking. Alternatively, if other muscles are used to keep the position of the hyoid bone fixed, then the mylohyoid muscle depresses the mandible. [1] It also functions as reinforcing the floor of mouth. [1]
The platysma muscle is a broad sheet of muscle arising from the fascia covering the upper parts of the pectoralis major muscle and deltoid muscle. Its fibers cross the clavicle, and proceed obliquely upward and medially along the side of the neck. This leaves the inferior part of the neck in the midline deficient of significant muscle cover. [1]
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.