be. When the conjunctiva becomes inflamed it is called
(Conjunctiv(a)itis) conjunctivitis. The sclerotic-cornea forms the
external tunic (coat) of the eyeball, the sclerotic being opaque and
forming the posterior five-sixths of the globe; the cornea, which forms
the remaining sixth (the front white part that is plainly seen) being
transparent. The sclerotic (means dense and hard) serves to maintain the
form of the globe, the eyeball.

[EYE AND EAR 347]

The cornea.--This is almost circular in shape. It is convex anteriorly and
projects forward from the sclerotic in the same manner that a watch glass
does from its case. This layer covers what we call the pupil.

The second tunic or coat (membrane) is formed from behind forward by the
Choroid, the ciliary body and the Iris. The choroid is the vascular and
dark coat covering the posterior five-sixths of the globe. The ciliary
body connects the choroid to the circumference of the iris. The iris is
the circular muscular septum (division) which hangs vertically behind the
cornea, presenting in its center a large rounded opening, the pupil.

The choroid is a thin highly vascular membrane of a dark brown or
chocolate color and is pierced behind by the optic nerve and in this
situation is firmly adherent to the sclerotic.

The ciliary body comprises three muscles for its make-up and connects the
choroid to the circumference of the iris.

The Iris (rainbow) has received its name from its various colors in
different individuals. It is a thin, circular shaped, contractile curtain,
suspended in the aqueous (watery) humor behind the cornea and in front of
the lens, being perforated a little to the nasal (nose) side of its centre
by a circular opening, the pupil, for the transmission of light. By its
circumference it is continuous with the ciliary body, and its inner or
free edge forms the margin of the pupil. The anterior surface of the iris
is variously colored in different individuals and marked by lines which
converge toward the pupil.

The Retina.--This is a delicate membrane, upon the surface of which the
images of external objects are received. Its outer surface is in contact
with the choroid; its inner, with the vitreous (glass) body. Behind it is
continuous with the optic nerve; it gradually diminishes in thickness from
behind forward. The retina is soft, semi-transparent and of a purple tint
in the fresh state. Exactly in the centre of the posterior part of the
retina