The junctions of the eye-lids are called the internal and external canthus, or angle of the eye.
They are opened by the levator palpe brx lifting up the upper lid ; and this mus cle is in a state of constant action so long as we keep our eyes open. They are closed by the circular orbicularis palpe brarum.
The cilia, or eye-lashes, are two rows of strong curved hairs implanted in the op posed edges of the two eye-lids, and ad mirably calculated for protecting the eye from dust or otherforeign bodies The hairy prominences above the eye lids are the sup ercilia, or eye-brows ; these are very moveable ; they serve as a pro tection to the eyes, and are much con cerned in expressing the passions.
In order to faciEtate the motions of the eye-lids and eye-balls on each other, the sutface of the conjunctiva is constantly moistened by a watery and mucilaginous fluid, poured out by the arteries ofthe part. The incrustations of the mucilage in the night would glue the eye-lids together ; but this effect is obviated by a natural oint ment, formed in a very elegant grandular apparatus on the inner surface ofthe tarsi. We there find about 16 or 17 longitudinal parallel rows of very minute glandular bo dies ; and these pour out their sebaceous secretion from a series of apertures on the edges of the eye-lids. They are called the meibomian glands, and ciliary- ducts.
The fluid just described is constantly formed on the suiface of the conjunctiva ; but on extraordinary occasions, as when an irritating foreign body is in the eye, or in consequence of affections of the mind, a fluid is poured out in greater abundance, which has the name of tears, andis secre ted by the lacrymal gland. This is a small
conglomerate gland, situated in the orbit, near the upper eye-lid, and having ducts which terminate on the surface of th e con junctiva ; but which, on account of their minuteness,are hardly demonstrable in the human subject. The utility of this secre tion in washing away any foreig-n substance must be sufficiently obvious.
The'superfluous part of the lacrymal se cretion is conveyed through two very fine tubes to a small bag, situated at the inter nal angle of the eye. These tubes com mence by open mouths, called the puncta lacrymali a, from the inner extremities of the ey-e-lids, and are about equal in sizeto admit a hog's bristle.
There is a little flesby projection at the corner of the eye, and between the two puncta, called caruncula lacrymalis.
The lacrymal sac is a small membranous bag, placed in the hollow formed at tbe inner edge of the orbit. The tendon of the orbicularis palpebrarum, which gene rally forms a slight eminence visible through the skin, crosses the middle of this bag.
A canal, called the ductus nasalis, and lodged in a groove of the superior maxilla ry bone, conveys the tears into the nose; where it terminates by an open orifice within the inferior turbinated bone.