The attachments of orbicularis oculi. The orbicularis oculi, the muscle of the squint, has three parts, with separate functions. The inner, eyelid part, the palpebral portion (A), runs crosswise through the lids and attaches at the eye corners, along with the lids (B and C). The outer, orbital por tion has its fixed attachment on the skull (D) and its.free attachment into the skin of the cheek. It has a lower half (E) and an upper half (F), which are semi-independent. Also pictured is levator palpebrae, eyelid lifter, with its fixed attachment to orbit (G), and its insertion on eyelid.
When the entire lower portion of orbicularis oculi contracts, the narrowing of the eye is combined with the bulging of the cheeks. This is a key action in the smile.
The area above the eye is completely relaxed (A). This contraction affects only the eyelids and the area below and beside the eye.
The eyes narrow . Now the lower lid is virtually a straight line and has begun to cover part of the lower pupil; the upper lid, not affected, is still above the pupil's upper edge.
Wrinkles (the "crow's feet") radiate out from the outer eye corner like spokes on a wheel. They follow closely the contours of the surface beneath. These, and the crease be low the eye, are the signature wrinkles of the orbicularis oris.
The wrinkling starts where upper lid line ends. Each line (B) tips progressively more downward, fading out as they pass to the side plane of the face. The last and lowest wrinkle emerges from the outer end of the little smile-shaped fold.
The cheek swells, particularly the upper half. Above the cheek, the little smile-shaped fold (C) or folds appear. Above it, the lower lid has a full look.
The crease from the nose to the mouth (the nasolabial fold) is deepened (D). If the pull is strong enough, the corner of the mouth may rise.
The upper half of the orbicularis oculi is not as free to move as the lower half because many of its fibers are intermingled with the fibers of such other muscles as the frontalis and the cor-rugator. But when it does contract, the whole upper part of the eye region is reshaped.
Keeping one eye open, look at yourself squeezing one eye tightly closed. Watch the inside end of the eyebrow. As soon as it starts to be pulled down, you know that you've started adding the action of the upper half of the orbicularis to the action of the eyelid and lower portions. In the upper eye area, the skin above the upper lid is shoved downward, hiding most of the upper lid itself. The lower lid is pressed upward from below, and the two lids meet in the line of the eyelashes.
Wrinkles radiate out from the inner corner of the eye like deeper mirror images of the crow's feet. One or two particularly deep folds may join their counterparts clear across the nose. They're not pretty. (Neither are the circumstances under which we use this muscle.)
The eyebrow7 is also pulled down, especially at its inner end. You can look at the muscle diagram and see why; the top part is right underneath the brow, so the brow is pulled toward the inner eye corner along with everything else. The corrugator may also be triggered, adding its pull to that of the orbicularis.
The net effect of the contraction is of an explosion of lines radiating out from the inner eye corner. The feeling is of compression and stress. The nose-to-mouth crease is greatly deepened; the nose itself is pulled upward, distorting the tip and creating horizontal creases along its length. And the pull on the corner of the mouth is much greater. The crow's feet and lower eyelid wrinkles also get much deeper.
One way to think about the muscle portions just described is that their actions appear in stages: the first stage, using the palpebral portion, just narrows the eye a little; the second stage, using the orbital's lower half, starts a true squint, a pleasant-looking one; the third stage, using the whole muscle, squeezes the eye for all it's worth, leading to a pained expression.
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