Incisivus labii inferioris muscle

Last revised by Daniel J Bell on 15 Nov 2021

The incisivus labii inferioris muscle (TA: pars labialis musculi orbicularis oris) is one of the facial muscles. It acts as a supplementary muscle to the orbicularis oris muscle.

The incisivus labii inferioris muscle is often omitted from major anatomical texts or articles on the facial muscles. This is because many consider it, including the Terminologia Anatomica, to be a labial component of the orbicularis oris muscle rather than a muscle in its own right 1,4.

The incisivus labii inferioris muscle originates from the buccal aspect of the mandible, specifically the incisive fossa, a shallow depression lying just inferior to the lateral incisor tooth on each side. The origin lies laterally adjacent from where mentalis muscle arises, usually with blending of the fibers of the two muscles. The muscle runs superiorly and laterally to merge with fibers of the orbicularis oris muscle, with some fibers terminating in the modiolus. Fibers from incisivus labii inferioris also support the deep portion of buccinator muscle 1,2,5.

A novel - recently described - facial space, the buccomandibular space has the incisivus labii inferioris muscle as part of its entrance and anterior aspect 3.

  • pulls the oral commissures, and thus the lips, towards the midline
  • in concert with orbicularis, incisivus effects pouting of the lips

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