The depressor anguli oris muscle is attached to the lower jaw (mandible). It ends at the orbicularis oris, which is the ring-like muscle that encompasses the lips. It is attached at the edge of the lips. The depressor anguli oris muscle is associated with frowning, as it works to pull down the edges of the lips. This is a paired set of muscles, with one on either side of the mouth.
The depressor anguli oris muscle sometimes does not develop in utero, meaning the baby is born without the muscle. This absence is not noticeable when the baby is quiet; however, when crying a facial asymmetry is visible. The corner of the mouth on the side where the muscle is normal pulls down but the side where it is missing does not. The condition is usually not treated with surgery because when the child is older, the asymmetry will not be noticeable.
The depressor anguli oris muscle is the muscle that produces what are commonly known as the jowls of the face. A small amount of Botox can be injected into this muscle to remove what may appear in some people to be a perpetual frown.