Top: The palpebral fissure (1) is bounded by superior (2) and inferior (3) palpebrae (eye lids). The fissure is also bounded by a medial commissure (4) and a lateral commissure (5). An orbicularis oculi m. (6) within the lids closes the palpebral fissure. A retractor angularis occuli m. is also evident (7).
Bottom: Enlarged view. A plica semilunaris, commonly called the third eyelid (8), partially obscures the cornea (9) and sclera (10) of the eyeball. The sclera is coated by bulbar conjunctiva. The eyelids, including the third eyelid, are lined by palpebral conjunctiva. Conjunctival sac refers to the space between the eyelids and eyeball. Lacrimal caruncle (11) refers to tissue at the medial commissure. Dorsal (12) and ventral (13) lacrimal puncta are openings for drainage of tear secretion.