466
UNIT THREE
In the back of the eye, the
optic
(op
tik)
nerve
and blood
vessels pierce the sclera. The dura mater that encloses these
structures is continuous with the sclera.
The Middle Tunic
The middle, or vascular, tunic of the eyeball (uveal layer)
includes the
choroid coat,
the ciliary body, and the iris. The
choroid coat, in the posterior F ve-sixths of the globe of the
eye, loosely joins the sclera. Blood vessels pervade the choroid
coat and nourish surrounding tissues. The choroid coat also
contains abundant pigment-producing melanocytes that give
Ciliary body
Retina
Choroid coat
Sclera
Fovea centralis
Vitreous humor
Optic nerve
Lens
Iris
Pupil
Cornea
Aqueous
humor
Anterior
cavity
Anterior
chamber
Posterior
chamber
Suspensory
ligaments
Lateral rectus
Medial rectus
Optic disc
Posterior cavity
FIGURE 12.25
Transverse section of the right eye (superior view).
Conjunctiva
Posterior
chamber
Suspensory
ligaments
Vitreous
humor
Iris
Lens
Ciliary process
Ciliary muscles
Ciliary
body
Sclera
Cornea
Anterior chamber
FIGURE 12.26
Anterior portion of the eye.
it a brownish-black appearance. The melanin of these cells
absorbs excess light and helps keep the inside of the eye dark.
The
ciliary body,
which is the thickest part of the mid-
dle tunic, extends forward from the choroid coat and forms
an internal ring around the front of the eye. In the ciliary
body are many radiating folds called
ciliary processes
and
two distinct groups of muscle F
bers that constitute the
cili-
ary muscles.
Figure 12.26
shows these structures.
Many strong but delicate F
bers, called
suspensory liga-
ments
(zonular F bers), extend inward from the ciliary pro-
cesses and hold the transparent
lens
in position. The distal
ends of these F
bers are attached along the margin of a thin
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