Incisivus labii superioris muscle

The incisivus labii superioris muscle, situated in the facial region, serves primarily in retracting the upper and lower lips. 'Incisivus' derives from the Latin 'incidere' meaning 'to cut through.'

Summary

• origin: incisive fossa of the maxilla

• insertion: orbicularis oris muscle

• blood Supply: facial and maxillary arteries

• innervation: facial nerve (CN VII)

• action: retracts upper and lower lips

Gross anatomy

Origin

The incisivus labii superioris muscle originates in an oblique and linear pattern through the floor of the incisive fossa of the maxilla. It interweaves with the peripheral part of the orbicularis oris muscle, partially blending with the levator anguli oris muscle, before attaching to the modiolus.

Insertion

The muscle finds its insertion in the orbicularis oris muscle and the modiolus, serving as anchorage for its function in lip retraction.

Arterial supply

Oxygenated blood is supplied primarily through the facial arteries. Additional supply comes from a few branches of the infraorbital extensions of the maxillary arteries.

Venous drainage

Venous drainage is via the facial vein and some tributaries of the infraorbital vein, both of which typically drain blood from the facial muscles.

Innervation

Innervation to the incisivus labii superioris muscle is facilitated by the facial nerve (CN VII), enabling its role in facial expressions.

Action

The primary function of the muscle is the retraction of both the upper and lower lips, in concert with the orbicularis muscle. This muscle also facilitates the pouting of the lips and acts as the "direct tractor" of the upper lips, playing a vital role in forming facial expressions.