Conjunctiva

The "conjunctiva" is a mucous membrane that lines the inner surfaces of the eyelids and folds back to cover the front surface of the eyeball, except for the central portion of the eye (the "cornea"). Although the conjunctiva that lines the eyelids is pretty thick, the part on the eyeball is very thin. It is also very movable and quite transparent, so that blood vessels are clearly visible below it.