r pulley over which one of the muscles passes. The bone is
seen above and below the eye.]

_Observation._ If the external muscle is too short, the eye is turned
out, producing the "wall eye." If the internal muscle is contracted,
the eye is turned inward toward the nose. It is then called a "cross
eye."

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905. How many muscles has the eye? Give their attachments. What causes
the pearly appearance of the eye? What does fig. 140 represent? What
is the effect if the external muscle is contracted? The internal
muscle?

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906. The PROTECTING ORGANS are the _Or'bits_, _Eyebrows_, _Eyelids_,
and _Lach'ry-mal Apparatus_.

907. The ORBITS are deep, bony sockets, in which the globes of the
eyes are situated. They have the form of a cone, the base of which is
open and directed forward. The bottom of the orbits is pierced by a
large hole which gives passage to the optic nerve. These cavities are
lined with a thick cushion of fat, in order that the eyes may move in
all directions, with perfect freedom and without friction.

908. The EYEBROWS are two projecting arches of integument, covered
with short, thick hairs, which form the upper boundary of the orbits.
The eyebrows are so arranged that they prevent the moisture that
accumulates on the forehead, in free perspiration, from flowing into
the eye, and also shade these organs from too vivid light.

909. The EYELIDS are two movable curtains placed in front of the eye.
They have a delicate skin on the outside, muscular fibres beneath, and
a narrow cartilage on their edges, which tends to preserve the shape
of the lid. Internally, they are lined by a smooth membrane, which is
reflected over the front of the eye upon the sclerotica. This membrane
is called the _con-junc-ti'va_. It secretes the fluid that moistens
and lubricates the eye, and which causes the eyelids to open and shut
without friction.

_Observation._ When the portion of this membrane that is reflected
over the globe of the eye, is inflamed, there is frequently a
deposition of whitish material, called lymph. This accounts for the
films, opacities, and white spots seen upon the eye after the
inflammation has subsided.

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906. Name the protecting organs of the eye. 907. Describe the orbits.
How are the movements of the eye facilitated? 908. Describe the
eyebrows. What does this arrangement prevent? 909. Describe the
eyelids. What i