Is the muscle of Horner part of the orbital or palpebral portion of the orbicularis oculi?

The muscle of Horner, also known as the muscle of Horner or the palpebral portion of the orbicularis oculi, is primarily involved in the act of closing the eyelids gently. It plays a significant role in eyelid function, particularly in maintaining the closure of the eyelid during sleep and during blinking.

The palpebral portion of the orbicularis oculi is specifically responsible for this action, as it lies within the eyelid itself and is more involved in the delicate actions of blinking and gentle eye closure. This portion receives innervation from the facial nerve and assists in protecting the eye surface from potential irritants and excessive light exposure by enabling controlled closure.

In contrast, the orbital portion of the orbicularis oculi is more associated with the strong closure of the eyelid when necessary, such as during protection against bright lights or foreign bodies. Therefore, the muscle of Horner is classified as part of the palpebral portion, aligning with its specific function in eyelid movement.