The posterior part of the orbital margin is formed chiefly by the
orbital ligament, which extends from the extremely short supraorbital
process to the small eminence at the junction of the malar and the
zygomatic process of the temporal.
Cilia occur only on the upper eyelid. The inner canthus is prolonged by
a groove on the infraorbital region. The tarsal glands are very short
and curved. The conjunctival epithelium is of the transitional type with
many goblet cells.
The deep part of the cartilage of the third eyelid is broad and
spoon-like, the superficial part somewhat anchor-shaped. In addition to
the gland which surrounds the deep part of the cartilage, there is a
deeper gland of Harder (Glandula palpebræ tertiæ profunda), which is
surrounded by a distinct capsule and a blood-sinus. This gland is
brownish or yellowish-gray in color, elliptical in outline, and about an
inch (2 to 3 cm.) in length. It is situated deeply below the attachment
of the inferior oblique muscle.
The caruncula lacrimalis has the form of a ridge; it divides into two
branches which join the skin at the inner commissure. It is red in color
and contains numerous large coil glands.
The lacrimal gland is mucous in type. There is no lacrimal sac, and the
two lacrimal ducts pass through separate openings at the infraorbital
margin. The naso-lacrimal duct is usually short and opens into the
inferior meatus at the posterior end of the inferior turbinal.[229]
The eyeball appears small, partly on account of the narrowness of the
palpebral opening; it closely approaches the spherical form. The cornea,
although in reality almost circular, appears oval when viewed from the
front, the inner end being much the broader. The chorioid has no
tapetum. The iris is usually dark grayish-brown or yellowish-brown, but
sometimes has a blue tinge. The pupil is a transverse oval in ordinary
light, but almost circular when dilated; granula are not present. The
optic papilla is nearer the posterior pole than in the horse and ox, and
has a distinct central artery and vein.