These consist of three distinct parts forming one unit which lifts the eyelid. The levator palpebrae superioris is a striated muscle that arises from the lesser wing of the sphenoid directly above the Annulus of Zinn in the posterior orbit. It runs forward under the orbital roof for 40mm before changing direction and splitting into two elements, the anteriorly placed aponeurosis and a thin strip of smooth muscle (Muller's).
The aponeurosis is a dense sheet of collagen fibres that runs towards the lid margin and inserts onto the anterior surface of the tarsal plate and also between orbicularis fibres anteriorly to form the skin crease. The aponeurosis also fans out medially and laterally into the horns. The lateral horn splits the lacrimal gland into orbital and palpebral lobes and inserts onto Whitnall's tubercle.The medial horn attaches to the medial orbital wall. Muller's muscle extends from the levator below the aponeurosis and in front of conjunctiva down to the tarsus and attaches to the superior edge of the tarsus by a 1mm tendon.
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