All birds, however, have not eyelids: hence it is, that those which are viviparous have no nictation of the eye. The heavier kinds of birds shut the eye by means of the lower eyelid, and they wink by drawing forward a membrane which lies in the corner of the eye. Pigeons, and other birds of a similar nature, shut the two eyelids; but the quadrupeds which are oviparous, such, for instance, as the tortoise and the crocodile, have only the lower eyelid moveable, and never wink, in consequence of the hardness of the eye. The edge of the upper eyelid was by the ancients called " cilium," from which comes our word "supercilia.[1]" If the eyelid happens to be severed by a wound it will not reunite,[2] which is the case also with some few other parts of the human body.