e lids are bordered with two or more rows of hairs
called the eyelashes, which serve both for ornament and for use. They
help to protect the eyes from dust, and to a certain extent to shade them.
Their loss gives a peculiar, unsightly look to the face.

The upper border of the orbit is provided with a fringe of short, stiff
hairs, the eyebrows. They help to shade the eyes from excessive
light, and to protect the eyelids from perspiration, which would otherwise
cause serious discomfort.

335. The Lacrymal Apparatus. Nature provides a special secretion, the
tears, to moisten and protect the eye. The apparatus producing this
secretion consists of the lacrymal or tear gland and lacrymal
canals or tear passages (Fig. 136).

Outside of the eyeball, in the loose, fatty tissue of the orbit, in the
upper and outer corner is the lacrymal or tear gland. It is
about the size of a small almond and from it lead several little canals
which open on the inner surface of the upper lid. The fluid from the gland
flows out by these openings over the eyeball, and is collected at the
inner or nasal corner. Here in each lid is a little reddish elevation, or
_lacrymal caruncle_, in which is an opening, communicating with a small
canal in the lid which joins the lacrymal sac, lodged between the
orbit and the bridge of the nose (Fig. 137).

From this sac there passes a channel, the nasal duct, about one-half
of an inch long, leading into the lower portion of the nostril. The fluid
which has flowed over the eye is drained off by these canals into the
nose. During sleep this secretion is much diminished. When the eyes are
open the quantity is sufficient to moisten the eyeball, the excess being
carried into the nose so gradually that the attention is not attracted to
it.

The lacrymal canals are at times blocked by inflammation of the nasal
duct, and the fluid collects in the corners of the eyelids and overflows
down the cheeks, producing much inconvenience. The lining membrane of the
eyelids through these canals is continuous with that of the nostrils.
Hence, when the lining membrane of the eye is red and swollen, as during a
cold, the nasal passages are also irritated, and when the nasal membrane
is inflamed, the irritation is apt to pass upwards and affect the eyelids.

336. The Tears. The lacrymal or tear gland is under the control of the
nervous system. Thus, if anything irritates the eyelids, the sensory
nerves are stimulated and the i