The posterior margin of the orbit is formed by the orbital ligament, as
in the pig. The orbital axes if produced backward would include an angle
of about 79°, the optic axes an angle of about 92.5° (Koschel).
The lower eyelid has no distinct cilia. The inner angle is wide, the
lacus lacrimalis shallow, and the caruncula lacrimalis small and
yellowish-brown. The conjunctival epithelium is cylindrical, with many
goblet cells. The gland which surrounds the deep end of the cartilage of
the third eyelid is large and pink; it is a mixed gland.
The lacrimal gland is flat and lies chiefly under the orbital ligament.
It is pink in color and mixed in structure. The naso-lacrimal duct is
variable in arrangement and may differ on the two sides. It may open
into the inferior meatus immediately after its emergence from the
osseous lacrimal canal; thence it continues forward and opens on the
lateral wall of the nostril below the inferior turbinal fold.
The eyeball is almost spherical and is relatively large, especially in
the small breeds. The sclera is thick in the ciliary region, where it
contains a well-developed venous plexus; in the vicinity of the equator
it is thin, and the chorioid shows through it. The cornea is almost
circular. The chorioid is richly pigmented, and presents a well defined
=tapetum cellulosum=; this is somewhat triangular in outline and has a
metallic luster. Its color is often golden green, shading to blue
peripherally, but the blue tone may predominate, and in other cases it
is mainly golden yellow or reddish-yellow. The appearance is due to
several layers of peculiar flattened polygonal cells. The ciliary muscle
is more developed than in the other species. The iris is commonly light
or yellow brown, but not rarely has a blue tinge; the color often
differs in the two eyes. The pupil is round; its edge is either smooth
or bears minute round prominences. The retina presents a round area
centralis external to the optic papilla. The latter is variable in
outline; commonly it has the form of a triangle with the angles rounded
off, but is often round or oval. Branches of the central vessels of the
retina radiate from the middle of the papilla. The surfaces of the lens
are not so strongly curved as in the other domestic animals, and there
is little difference in the radius of curvature of the two surfaces.