{{Short description|Facial muscle that depresses the corner of the mouth during frowning}} {{No footnotes|article|date=May 2015}} {{Infobox muscle | Name = Depressor anguli oris | Latin = musculus depressor anguli oris | Image = Gray381.png | Caption = Scheme showing arrangement of fibers of Orbicularis oris (triangularis labeled at bottom right). | Image2 = Depressor anguli oris.png | Caption2 = Muscles of the head, face, and neck (labeled as triangularis near chin). | Origin = Tubercle of mandible | Insertion = Modiolus of mouth | Action = Depresses angle of mouth | Blood = Facial artery | Nerve = Marginal mandibular branch of the facial nerve }} The '''depressor anguli oris muscle''' ('''triangularis muscle''') is a facial muscle. It originates from the mandible and inserts into the angle of the mouth. It is associated with frowning, as it depresses the corner of the mouth.
== Structure == The depressor anguli oris arises from the lateral surface of the mandible.<ref name=":0">{{Cite journal|date=2004-09-01|title=Depressor labii inferioris resection: an effective treatment for marginal mandibular nerve paralysis|url=https://www.sciencedirect.com/science/article/abs/pii/S0007122604001043|journal=British Journal of Plastic Surgery|language=en|volume=57|issue=6|pages=502–510|doi=10.1016/j.bjps.2004.04.003|issn=0007-1226|last1=Hussain |first1=G. |last2=Manktelow |first2=R.T |last3=Tomat |first3=L.R |pmid=15308395 |url-access=subscription}}</ref> Its fibers then converge. It is inserted by a narrow fasciculus into the angle of the mouth.<ref name=":0" /> At its origin, it is continuous with the platysma muscle, and at its insertion with the orbicularis oris muscle and risorius muscle. Some of its fibers are directly continuous with those of the levator anguli oris muscle, and others are occasionally found crossing from the muscle of one side to that of the other; these latter fibers constitute the transverse muscle of the chin.
The depressor anguli oris muscle receives its blood supply from a branch of the facial artery.
=== Nerve supply === The depressor anguli oris muscle is supplied by the marginal mandibular branch of the facial nerve.<ref name=":0" />
== Function == The depressor anguli oris muscle is a muscle of facial expression.<ref name=":0" /> It depresses the corner of the mouth, which is associated with frowning.<ref name=":0" />
== Clinical significance ==
=== Paralysis === Damage to the marginal mandibular branch of the facial nerve may cause paralysis of the depressor anguli oris muscle.<ref name=":0" /> This may contribute to an asymmetrical smile.<ref name=":0" /> This may be corrected by resecting (cutting and removing) the depressor labii inferioris muscle, which has a more significant impact on smiling.<ref name=":0" />
===Hypoplasia/aplasia=== Underdevelopment (hypoplasia) or complete absence (aplasia) of the depressor anguli oris can occur.<ref>{{cite web | url=https://www.medicalnewstoday.com/articles/hypoplasia#similar-conditions | title=Hypoplasia: Where it can occur, causes, effects, and treatment options | date=13 November 2020 }}</ref> Similarly to paralysis, individuals with these conditions will have an asymmetric smile.{{medical citation needed|date=July 2023}} These conditions are rare, and develop at or before birth (congenitally).
== See also == * Facial muscles * Transverse muscle of the chin
== Additional images == {{Cleanup-gallery anatomy|date=May 2015}} <gallery> File:Depressor anguli oris animation small.gif|Position of depressor anguli oris muscle File:Gray176.png|Mandible, outer surface, side view File:Gray508.png|The arteries of the face and scalp </gallery>
== References == {{Gray's}} <references />
== External links == {{Commons category|Depressor anguli oris muscles}} * [https://web.archive.org/web/20050804024427/http://www.ptcentral.com/muscles/musclehead.html#depressor%20anguli%20oris PTCentral]
{{Muscles_of_head}} {{Portal bar|Anatomy}} {{Authority control}}
Category:Muscles of the head and neck Category:Facial muscles