The depressor anguli oris muscle (triangularis muscle) is a facial muscle. It originates from the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

and inserts into the angle of the

mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also 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 fr ...

, as it depresses the corner of the mouth.

Structure

The depressor anguli oris arises from the lateral surface of the

. Its

fiber Fiber (spelled fibre in British English; from ) 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 inco ...

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 or platysma 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 "bowst ...

, 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 not a true sphincter, as was once thought, as it is actually composed of four independent quadrants that interlace and give only an a ...

and

risorius muscle The risorius muscle is a highly variable muscle of facial expression. It has numerous and very variable origins, and inserts into the angle of the mouth. It receives motor innervation from branches of facial nerve (CN VII). It may be absent or a ...

. 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 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 origi ...

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

facial artery The facial artery, formerly called the external maxillary artery, is a branch of the external carotid artery that supplies blood to superficial structures of the medial regions of the face. Structure The facial artery arises in the carotid t ...

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 Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

facial expression Facial expression is the motion and positioning of the muscles beneath the skin of the face. These movements convey the emotional state of an individual to observers and are a form of nonverbal communication. They are a primary means of conveying ...

. 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 (: paralyses; also known as plegia) is a loss of Motor skill, motor function in one or more Skeletal muscle, muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory d ...

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 (; 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 asymmetric smile. 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