How are eyelids formed?

Answer 1

Interesting layman's explanation here:

http://www.YouTube.com/watch?v=AVxdRrWjh0g&feature=related

(4:50 ish; kinda neat)

Also:

http://www.medical-look.com/human_anatomy/organs/Eyelids_and_eyelashes.html

and

http://books.Google.com/books?id=nJwoAAAAYAAJ&pg=PA193&lpg=PA193&dq=how+eyelids+are+formed&source=bl&ots=tTyeALU5D1&sig=8RvME42jOY03o5pZLFJ9Jl_23wk&hl=en&ei=HLPbSvqsFo2sMMa6iNcH&sa=X&oi=book_result&ct=result&resnum=5&ved=0CB8Q6AEwBDgK#v=onepage&q=how%20eyelids%20are%20formed&f=false

Essentially, the eyelids are made of four membranous layers and of a sort of fibro-cartilage that keeps them able to hold their shape (it's what makes them feel sort of stiff if you try to bend them). The outermost layer (the one you can see) is the common integument and is really, really thin, almost translucent. It's very delicate and wrinkles easily. The tissue beneath the outermost skin is loose and sometimes filled with a sort of fluid that gives the eyelids a darker appearance (where undereye bags come from). Below that there is a layer of muscle which allows the eyelids to retract and close - this muscle layer is made up of a couple of different muscles; the orbicularis palpebrarum (in the lower eyelid) and the levator palpebrae superioris (in the upper one). Part of the layer of muscle, there is some fibrous tissue that sort of limits the range of motion of the eyelids. The last layer (which forms the "inner" surface of the eyelid - the part that touches our eye) is a very very thin, transparent mucus membrane called the tunica conjunctiva (heard of conjunctivitis or pink eye?).

Interesting stuff, at any rate. I'd like to find out more about this "cutting device" that separates the eyelids in the womb so that they're no longer just flaps of skin completely covering the eyes...