The =eyelids= are thick, prominent, and less pliable than those of the
horse. The lower lid bears a considerable number of cilia, which are,
however, finer than those of the upper lid. The tarsal glands are more
deeply embedded and therefore not so evident. The =conjunctiva= of the
lower lid presents folds or ridges, and one or two prominences which
contain numerous leukocytes; the conjunctival epithelium is transitional
in type. The superficial part of the cartilage of the =third eyelid= is
leaf or shovel-shaped and thicker than in the horse; the edge bears a
narrower process, on which there is a transverse bar, giving the
arrangement some resemblance to an anchor. The =gland= of the third
eyelid is very large—an inch or more in length—and may be divided into
two parts. The deep part is pink and consists of loose lobules, but the
much larger superficial part is more compact. There are two large and
several smaller excretory ducts. The subconjunctival tissue of the third
eyelid contains lymph nodules, which are specially numerous on the
bulbar side.
[Illustration:
FIG. 583.—EYE OF OX. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =lacrimal gland= is thick and distinctly lobulated. It is more or
less clearly divided into a thick upper and a thinner lower part
(Glandula lacrimalis superior, inferior). There are six to eight larger
excretory ducts and several smaller ones. The =naso-lacrimal duct= is
shorter than in the horse, and is almost straight. Its terminal part is
inclosed between two plates of cartilage, and it opens near the nostril
on the outer wall; the orifice is placed on the inner side of the alar
fold of the inferior turbinal, and is therefore not easily found.
[Illustration:
FIG. 584.—LEFT EYEBALL OF OX _in situ_, EXTERNAL VIEW.
_19_, Orbital fat. (After Ellenberger-Baum, Anat. für Künstler.)
]
The =eyeball= resembles that of the horse in shape, but is considerably
smaller.
The average transverse diameter is about 42 mm., the vertical diameter
41 mm., and the axis 36 mm. The angle between the axes is about 119°.
The =sclera= is often more or less pigmented; where non-pigmented it may
have a bluish tinge. The point of entrance of the optic nerve is about 2
mm. external to the vertical meridian, and about 7 mm. below the
horizontal meridian.
The thickness of the sclera is about 2 mm. at the posterior pole, 1
mm. at the equator, and 1.2 to 1.5 mm. near the cornea.
The =cornea= is thicker than that of the horse.
The =tapetum= of the chorioidea is extensive at the outer side, but is a
narrow strip internally. It has a metallic luster, shading from a
brilliant green to a deep blue; centrally it has a reddish sheen.
The =iris= is usually very dark colored. The granula form a continuous
series of small nodules along the upper margin of the pupil and are most
prominent centrally; they are very small on the lower margin.
The =optic papilla= is much smaller and is not so sharply defined on
ophthalmoscopic examination as that of the horse. Several relatively
large retinal arteries radiate from the center of the papilla to the
periphery of the retina. They may be seen to wind spirally around the
veins, which are very large.
The arteria centralis retinæ arises from a posterior ciliary artery
and divides close to the optic papilla into three branches usually; of
these the upper is larger than the two lateral branches. The retina is
more vascular than that of the horse; it has a round area centralis at
the inner side, which is continued outward by a narrow strip of a
similar histological structure.
The =vitreous body= is less fluid than that of the horse.