and two oblique. The retractor oculi envelops the optic nerve between the
brain and the ball of the eye and becomes attached upon the external face
of the sclerotic tunic. When this muscle contracts, it draws the globe back
into the orbit, away from the light. The superior, inferior, external, and
internal recti or straight muscles are attached to the back part of the
orbital sheath and spread forward in four bundles over the globe of the
eye, where they are inserted by a fibrous expansion into the sclerotic at
the margin of the cornea. When they act singly, they turn the globe either
upward, downward, inward, or outward. The great oblique, by its action,
pivots the eye inward and upward in the orbit. The small oblique turns the
eye outward and downward.

The eyelids are two movable curtains, superior and inferior, which cover
and protect the eye in front. They are attached to the circumference of the
orbit and have a convex external face formed by the skin and a concave
internal face molded on the anterior surface of the eye and are lined by
the conjunctiva, which is reflected above and below on the eyeball. The
border of each lid is slightly beveled on the inner side and shows the
openings of the Meibomian glands. These glands secrete an unctuous fluid,
which is thrown out on the border of the lids, the function of which is to
facilitate their movements and enable them to retain the tears in the
ocular cavity. The eyelid is composed of a fibrous inner membrane ending in
a stiff arch near the border, a muscle to close the lid, another to open
it, the skin externally, and the conjunctival mucous membrane internally.
The border of each lid is covered and protected by long hairs to prevent
floating particles of matter in the atmosphere from gaining entrance to the
eye.

The membrana nictitans, which is also named the third eyelid, winking
eyelid, haw, etc., is placed at the inner angle of the eye, whence it
extends over the eyeball to relieve it from foreign bodies which may fall
upon it. It has for its framework a fibro-cartilage, irregular in shape,
thick, nearly prismatic at its base, and thin anteriorly where it is
covered by the conjunctiva; behind, it is loosely attached to a fatty
cushion.

The lacrimal gland is situated between the orbital process and the upper
part of the eyeball. It secretes the tears destined to lubricate the
anterior surface of the eye. This fluid escapes upon the organ at the outer
angle of