The eye is provided with a nictitating membrane or third eyelid, at the base of which open the ducts of the Harderian gland.
In Elasmobranchii they are better developed, and the nictitating membrane is frequently present.
The moment after, the eye itself confirmed this—the nictitating membrane was rapidly drawn over it, and as rapidly removed.
In the Sauropsida all three eyelids are usually present, but in Mammalia the nictitating membrane is rudimentary.
Haw, haw, n. the nictitating membrane or third eyelid, as of a horse; also a disease of this membrane.
The eyes have a nictitating membrane, the nose is prominent and mobile, and the tail very short.
If any part of the nictitating membrane is visible below, it must be pushed up with the steel point.
The eyes are large, and have a third eyelid, or nictitating membrane, to draw across the pupil during the day.
In almost all mammals below the Primates there is a third lid, the nictitating membrane.
The sixth pair, nervus abducens, passes also to muscles of the eye, and in sharks to the nictitating membrane or third eyelid.