Depressor anguli oris muscle
Depressor anguli oris is a paired triangular muscle that extends from the mental tubercle of mandible to the angle of the mouth. It belongs to the buccolabial group of facial muscles along with levator labii superioris alaeque nasi, levator labii superioris, zygomaticus major, zygomaticus minor, levator anguli oris, risorius, depressor labii inferioris, mentalis, orbicularis oris, incisivus superior, incisivus inferior and buccinator muscles.
The muscle is situated lateral to the chin on each side, extending almost vertically upwards. Along with other muscles that attach at the angle of the mouth, depressor anguli oris forms a fibromuscular structure called modiolus.
As its name suggests, it depresses (depressor) the angle of the mouth (anguli oris) and pulls it slightly laterally. Thereby, it facilitates expressing sadness and assists in opening the mouth.
|Origin||Mental tubercle and oblique line of mandible (continuous with platysma muscle)|
|Function||Depresses angle of mouth|
|Innervation||Buccal and mandibular branches of facial nerve (CN VII)|
|Blood supply||Inferior labial artery (facial artery); mental artery (maxillary artery)|
This article will teach you all you need to know about the anatomy and functions of depressor anguli oris muscle.
Origin and insertion
Depressor anguli oris originates from the oblique line and mental tubercle of mandible located on the anterior aspect of the bone. The muscle fibers converge into a narrow fascicle running superiorly towards the angle of the mouth. It then blends with other muscles that insert into the lips. On the point where all of these muscles converge and interlace they form a dense, mobile, fibromuscular mass called the modiolus. It is not entirely clear which muscles exactly attach to the modiolus, but some of the certain ones include depressor anguli oris, buccinator, risorius, zygomaticus major and orbicularis oris muscles.
Some fibers of the depressor anguli oris muscle can continue below its origin point at the mental tubercle and cross the midline to blend with the contralateral fibers. These particular fibers form the transversus menti muscle, also called the “mental sling”.
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Depressor anguli oris arises from the anterior side of the mandible as one of the superficial layer muscles of the buccolabial group. The distal part of the muscle courses over the lateral border of depressor labii inferioris. Inferiorly, depressor anguli oris is continuous with the platysma muscle and cervical fascia.
Depressor anguli oris receives motor innervation from marginal mandibular and buccal branches of facial nerve (CN VII).
Depressor anguli oris is supplied by the inferior labial and mental arteries, which are branches of the facial artery and maxillary artery, respectively. The venous blood is drained through the facial vein into the internal jugular vein.
Depressor anguli oris pulls the angle of the mouth inferolaterally. Its action plays an important part in facial expression, as it helps expressing feelings of sadness or anger. This is why depressor anguli oris is deemed one of the “frowning muscles”, along with muscles such as corrugator supercilii, procerus and orbicularis oris. Depressor anguli oris also aids in functions such as opening the mouth while speaking or eating. While opening the mouth, the action of depressor anguli oris modifies the mentolabial sulcus, making it deeper and more horizontal.
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