Special Senses

Abstract

The eyelids (palpebrae) are two thin, movable folds, the upper being the larger, more movable and furnished with a muscle known as the levator palpebrae superioris, which elevates the lid. Both eyelids are covered by skin superficially and by mucous membrane (conjunctiva) over the deep aspect. When the eye is opened an elliptical space, the palpebral fissure, remains between the lid margins. The lids are united laterally and medially by corresponding palpebral ligaments (canthi). The lateral palpebral ligament (external canthus) is more acute than the medial and is placed directly against the globe (Fig. 51). The medial ligament, or internal canthus, is prolonged for a short distance toward the nose, and here the 2 eyelids are separated by a triangular space known as the tear lake (lacus lacrimalis). This lacus is bounded above and below by the lacrimal parts of the eyelid and laterally by a crescentic fold of conjunctiva known as the plica semilunaris, which is considered as a remnant of the third eyelid. In the lacus there is a reddish elevation, the caruncle, composed of modified skin and containing a few fine hairs, sebaceous and sweat glands.