Head and neck muscles (chewing, facial, and throat muscles)

Depressor Anguli Oris

Musculus depressor anguli oris (triangularis)

Origin

Inferior border of the mandible, below the first and second molars

Insertion

Angle of the mouth, interweaving with the orbicularis oris and levator anguli oris muscles

Function

Pulls the corner of the mouth downward and laterally, as in sadness

Innervation

Marginal mandibular branch of the facial nerve (CN VII)

Movement & chain

Pulls the corner of the mouth downward and slightly laterally; a mimetic movement that acts opposite to the levator anguli oris and zygomaticus major muscles.

Palpation

Palpable as a narrow band from the inferior border of the mandible to the corner of the mouth when actively pulling the corner of the mouth downward.

Clinical

Isolated failure of exactly this branch (e.g. from a superficial injury or parotid surgery) causes an asymmetric corner of the mouth without affecting the rest of the face: a classic pitfall when distinguishing a 'true' facial palsy.

Segmental innervation

CN VII, motor.

In clinical practice

Depresses the oral commissure; targeted botulinum toxin injection to treat asymmetrical lower lip smile and marionette lines.

Region in the model

Head and neck muscles (chewing, facial, and throat muscles)