together with the other oblique muscle, then causes the eye to roll outwards, as in the effort to perceive a distant mountain or an island far

at sea.

The

In order further to facilitate the numerous motions of the eyeball, it is furnished with a constant supply of moisture from a gland called the lachrymal gland, situated within the upper and outer part of the bony socket. lachrymal gland is composed of a great number of small globular bodies, from which seven or eight ducts, not much thicker than a hair, run into the inner surface of the eyelid. In twentyfour hours, it has been computed that the two lachrymal glands discharge about four ounces of the fluid well known by the name of tears. The tears are very limpid, of a saltish taste, and when chemically analysed are found to contain water, mucus, common salt, and a very little soda and lime.

From the tears constantly running into the eyes, it is requisite there should be some contrivance to carry off any quantity which might be found superfluous; and for this purpose, when the eyelids come together in the incessant process of winking, they form a channel, which runs in front of the eye, having some

what of a sloping direction towards the nose, or the inner canthus. I may also remark, that the eyelids begin first to touch each other at the outer angle, and the pressure proceeds successively to the inner, and this consequently impels the tears along the channel towards the inner canthus.

As soon as the tears have reached the end of the channel, there is a passage for them through the puncta lachrymalia in two directions, -one above and another below the corner of each eye. Each of these puncta consists of a minute foramen, or hole, with a whitish cartilaginous circle around it, capable of admitting a bristle or a small pin, and placed on the very point of the angle of the eyelid, opposite the last hair of the eyelash towards the inner canthus. These puncta absorb the tears, not, as has been supposed, by the mysterious power termed capillary attraction, but by the same vital power as the lacteals of the intestines take up the chyle and carry it into the blood through the channel of the thoracic duct.

The puncta lachrymalia lead to two canals, just wide enough to admit a bristle, running above and below the sides, which form the

angle of the eye at the canthus, in the shape of a bifurcation, till they reach the nose, where they unite into one, and form the lachrymal sac. The ducts thus united now take a downward course along the exterior parietes of the nose for about an inch; and the lachrymal duct here penetrates the bone, and discharges the tears into the side of the base of the nose, about an inch from the orifice of the nostril. Here the superfluous moisture is carried off by the stream of air constantly passing in the act of respiration.

The palpebra, or eyelids, are lined on their internal surface with a very delicate skin, full of ramified blood-vessels. This is termed the conjunctiva, and is considerably larger than the parts it covers, and loose, so as to admit of motion.

Besides the tears, the eyes are furnished with a sebaceous substance readily soluble. This is secreted in certain beautiful little glands, interspersed within the conjunctiva of the inner eyelid, near the roots of the eyelashes, appearing under the microscope like small pearls. According to M. Majendie, it is prepared in these glands, and is of a glairy consistence, of the nature of albumen, and capable of being dis

solved in the tears. It may be supposed to be intended to neutralise the acrimony of the salts contained in the tears, which might, without this addition, prove too harsh for the eye. During sleep, when the tears are deficient in quantity, this substance is not dissolved, but is collected in the corners of the eyes; and sometimes, when it is abundant and thicker than usual, it glues the eyelids together.

This substance, together with the tears in which it is dissolved and diluted, is constantly spread over the eyeball by the sweep of the eyelids, which act like valves, and are composed of semi-transparent muscular membrane, attached to the cartilage that is articulated with the adjacent bone of the socket, giving them firmness, and preserving their shape. Under the skin here, there is a thin fluid, which, after excess of fatigue, as well as a consequence of various diseases, becomes thicker and more abundant, and gives the eyelids a dark leaden hue, which, whenever it appears, is a sure mark of exhaustion and weakness.

The eyelids are elegantly fringed with short hairs, termed cilia, or eyelashes, either to defend the eye from any thing falling into it, or to modify the effect of the rays of light. When

these hairs are removed, the sight is always impaired. When they are wet with tears, the little drops act upon the light like dew-drops, and produce beams of iridescent colours.

When the eye is opened, the upper eyelid only is raised-an effect produced by the action of a small fan-shaped muscle attached to the inner part of the bone of the socket. The eye is shut by another muscle, which surrounds the eyelids, and is termed the orbicularis palpebrarum.

At the inner canthus of the eye there is a little red fleshy membrane, named the caruncula, in the form of a half-moon, which, when the eye is turned away, is spread over its inner part; and when any dust has fallen upon the ball, it sticks to this, and is carried into the corner of the eye by the membrane folding back. All dust and offensive matter is, by this means, thrown out at the corner of the eye, beyond the small holes of the entrance to the lachrymal ducts, otherwise these might be obstructed. The caruncula is formed of seven or eight folds, arranged in a semicircle, and studded with small hairs. The use of these hairs appears to be to throw out dust, or other foreign bodies, carried thither by the mechanism