The depressor anguli oris muscle (triangularis muscle) is a

facial muscle The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, alt ...

. It originates from the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bon ...

and inserts into the angle of the

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...

. It is associated with

frowning A frown (also known as a scowl) is a facial expression in which the eyebrows are brought together, and the forehead is wrinkled, usually indicating displeasure, sadness or worry, or less often confusion or concentration. The appearance of a fro ...

, as it depresses the corner of the mouth.

Structure

The depressor anguli oris arises from the lateral surface of the

. Its

fibre Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorpora ...

s then converge. It is inserted by a narrow fasciculus into the angle of the

. At its origin, it is continuous with the

platysma muscle The platysma muscle is a superficial muscle of the human neck that overlaps the sternocleidomastoid. It covers the anterior surface of the neck superficially. When it contracts, it produces a slight wrinkling of the neck, and a "bowstring" effe ...

, and at its insertion with the

orbicularis oris muscle In human anatomy, the orbicularis oris muscle is a complex of muscles in the lips that encircles the mouth. It is a sphincter, or circular muscle, but it is actually composed of four independent quadrants that interlace and give only an appearance ...

and

risorius muscle The risorius muscle is a muscle of facial expression. It arises from the fascia over the parotid gland, and inserts into the angle of the mouth. It is supplied by the facial nerve (CN VII). It may be absent or asymmetrical in some people. It retr ...

. Some of its fibers are directly continuous with those of the

levator anguli oris muscle The levator anguli oris (caninus) is a facial muscle of the mouth arising from the canine fossa, immediately below the infraorbital foramen. It elevates angle of mouth medially. Its fibers are inserted into the angle of the mouth, interminglin ...

, 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 transversus menti, or transverse muscle of the chin, is a facial muscle that is often considered to be the superficial fibers of the depressor anguli oris The depressor anguli oris muscle (triangularis muscle) is a facial muscle. It origina ...

. The depressor anguli oris muscle receives its blood supply from a branch of the

facial artery The facial artery (external maxillary artery in older texts) is a branch of the external carotid artery that supplies structures of the superficial face. Structure The facial artery arises in the carotid triangle from the external carotid arter ...

Nerve supply

The depressor anguli oris muscle is supplied by the marginal mandibular branch of the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

Function

The depressor anguli oris muscle is a

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

facial expression A facial expression is one or more motions or positions of the muscles beneath the skin of the face. According to one set of controversial theories, these movements convey the emotional state of an individual to observers. Facial expressions are ...

. It depresses the corner of the mouth, which is associated with

Clinical significance

Paralysis

Damage to the marginal mandibular branch of the

may cause

paralysis Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 5 ...

of the depressor anguli oris muscle. This may contribute to an asymmetrical smile. This may be corrected by resecting (cutting and removing) the

depressor labii inferioris muscle The depressor labii inferioris (or quadratus labii inferioris) is a facial muscle. It helps to lower the bottom lip. Structure The depressor labii inferioris muscle arises from the lateral surface of the mandible. This is below the mental for ...

, which has a more significant impact on

smiling A smile is a facial expression formed primarily by flexing the muscles at the sides of the mouth. Some smiles include a contraction of the muscles at the corner of the eyes, an action known as a Duchenne smile. Among humans, a smile expresses d ...

Hypoplasia/Aplasia

Underdevelopment (

Hypoplasia Hypoplasia (from Ancient Greek ὑπo- ''hypo-'' 'under' + πλάσις ''plasis'' 'formation'; adjective form ''hypoplastic'') is underdevelopment or incomplete development of a tissue or organ.Aplasia Aplasia (; from Greek ''a'', "not", "no" + ''plasis'', "formation") is a birth defect where an organ or tissue is wholly or largely absent. It is caused by a defect in a developmental process. Aplastic anemia is the failure of the body to produ ...

) of the depressor anguli oris can occur.Similarly to paralysis, individuals with these conditions will have an assymetric smile.https://www.healthline.com/human-body-maps/depressor-anguli-oris-muscle#1 These conditions are rare, and develop at or before birth ( congenitally).

Additional images

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

References

External links

PTCentral
{{Authority control Muscles of the head and neck Facial muscles