|Levator palpebrae superioris||Corrugator|
The Levator palpebra superioris is described with the anatomy of the eye. The Orbicularis oculi (figs. 579, 581) is a broad, flat, elliptical muscle which occupies the eyelids or palpebrae, surrounds the circumference of the orbit, spreads over the temporal region, and downwards on the cheek. It consists of three main portions-orbital, palpebral and lacrimal.
The orbital portion of the Orbicularis oculi, of a reddish color and thicker than the palpebral portion, arises from the nasal part of the frontal bone, from the frontal process of the maxilla, and from the medial palpebral ligament, which interrupts the line of the bony origin. Its fibers form complete ellipses without interruption on the lateral side, the upper fibers blending with the Frontal belly of Occipitofrontalis and Corrugator.
The palpebral portion of the Orbicularis oculi is thin and pale; it arises from the medial palpebral ligament, chiefly from its superficial and partly from its deep surface, but not from its lower margin; it arises also from the bone immediately above and below the ligament. The muscular fibers sweep across the eyelids in front of the orbital septum and at the lateral commissure interlace to form the lateral palpebral raphe. A small bundle of very fine fibers lies close to the margin of each eyelid, behind the eyelashes; it is named the ciliary bundle.
The lacrimal portion of the Orbicularis oculi (Tensor tarsi) lies behind the lacrimal sac, but is separated from it by the lacrimal fascia. It arises from the fascia covering the lacrimal sac, from the tipper part of the crest of the lacrimal bone, and from the adjacent part of the lateral surface of the lacrimal bone (fig, 582). Passing laterally behind the lacrimal sac the muscle divides into an upper and a lower slip; some of the fibers of these slips are inserted into the tarsi of the eyelids and are closely related to the lacrimal canaliculi, but most of them are: continued across the eyelids in front of the tarsi and interlace in the lateral palpebral raphe.
The lateral palpebral raphe is a much weaker structure than the medial palpebral ligament, It is formed by the interlacing of the lateral ends of the palpebral fibers of the Orbicularis oculi, strengthened on its deep surface by the orbital septum. A few lobules of the lacrimal gland lie between it and the more deeply placed lateral palpebral ligament (Whitnall).
Nerve-supply.—The Orbicularis oculi is supplied by the temporal and zygomatic branches of the facial nerve.
Actions.–The Orbicularis oculi is the sphincter muscle of the eyelids. The palpebral portion acts involuntarily, closing the lids gently, as in sleep or in blinking; the orbital portion is subject to the will. When the entire muscle is brought into action, the slain of the forehead, temple, and cheek is drawn towards the medial angle of the orbit, and the eyelids are firmly closed. The skin thus drawn upon is thrown into folds, especially radiating from the lateral angle of the eyelids; these folds become permanent in old age, and form the so-called ‘crow’s feet.’ The Levator palpebrae superioris is the direct antagonist of this muscle since it raises the upper eyelid and exposes the front of the bulb of the eye. The lacrimal part of the Orbicularis oculi draws the eyelids and the papillae lacrimales medially, and directs them into the laces lacrimalis; at the same time it exerts traction on the lacrimal fascia and so dilates the lacrimal sac.
The Corrugator is a small pyramidal muscle, placed at the medial end of the eyebrow, deep to the Frontal belly of Occipitofrontalis and to the Orbicularis oculi. It arises from the medial end of the superciliary arch; and its fibers pass laterally and slightly upwards, and are inserted into the deep surface of the skin, above the middle of the orbital arch.
Nerve-supply.-The Corrugator is supplied by the temporal branches of the facial nerve,
Actions.—-The Corrugator draws the eyebrow medially and downwards, producing the vertical wrinkles of the forehead. It is the ï¿½frowningï¿½ muscle, and may be regarded as the principal muscle in the expression of suffering.
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