1. =Orbicularis oculi.=—This is a flat, elliptical, sphincter muscle,
situated in and around the eyelids, the portion in the upper lid being
much broader than that in the lower. The chief attachment is to the skin
of the lids, but some bundles are attached to the palpebral ligament at
the inner canthus and to the lacrimal bone. Its action is to close the
lids.
2. =Corrugator supercilii.=—This is a very thin, small muscle, which
arises over the root of the supraorbital process and spreads out in the
upper eyelid, blending with the orbicularis. Its action is to assist in
raising the upper lid or, especially in pathological conditions, to
wrinkle the skin.
3. =Malaris.=—This is a very thin muscle, which varies much in different
subjects. It extends from the fascia in front of the orbit to the lower
lid. Its action is to depress the lower lid.
The foregoing muscles receive their blood-supply from the facial,
transverse facial, supraorbital, and infraorbital arteries; the
nerve-supply is derived from the facial nerve.
4. =Levator palpebræ superioris.=—This slender, flat muscle is almost
entirely within the orbital cavity. It arises on the pterygoid crest,
passes forward above the rectus oculi superior and below the lacrimal
gland, and terminates in a thin tendon in the upper lid.
_Action._—To elevate the upper lid.
_Blood-supply._—Ophthalmic artery.
_Nerve-supply._—Oculomotor nerve.