The depressor anguli oris muscle (triangularis muscle) is a facial muscle. 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 bone ...

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 ...

. 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

. 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 incorporate ...

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, 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.

Function

The depressor anguli oris muscle is a

muscle Skeletal muscles (commonly referred to as muscles) are 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 types of mus ...

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

Clinical significance

Paralysis

Damage to the marginal mandibular branch of the facial nerve 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, which has a more significant impact on smiling.

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) 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