The Orbicularis palpebrarum is a broad, thin, ring shaped layer of muscle that covers the eyelid and the surrounding |orbit|. It extends from the bottom of the forehead down to the front of the cheek, and from the inside of the bridge of the |nose| outward to the temple. Because of its shape it is classified as a sphincter muscle. It can be divided into two parts: the palpebral portion and the orbital portion. The palpebral portion is thin and pale. It forms a series of concentric curves on the outer side of the eyelid. The palpebral portion acts involuntarily, closing the lids when blinking or during sleep. The orbital portion is thicker and of reddish color. The |fibers| of the orbital portion form a complete ellipse. The upper |fibers| blend with the |occipito-frontalis| and corrugator supercilli.
