ABSTRACT
The upper and lower eyelids enclose the palpebral aperture and join at the medial and lateral canthi. The palpebral aperture is about 30 mm horizontally in an adult and 10 mm vertically. The lateral canthus is acute, and the medial canthus is rounded and separated from the eye by a small bay, the tear lake (lacus lacrimalis), in which are a rounded elevation, the caruncle, and a vertical fold, the plica semilunaris. The caruncle contains sweat and sebaceous glands. The plica is the remnant of the third eyelid of lower animals.
