168 ANTHROPOLOGY. 
J; branch to the inferior oblique muscle ; ff, stronger branch to the external 
rectus muscle ; gh 1, separation of the lachrymal artery, and to the lachry- 
mal gland and upper eye-lid. Fig. 16, veins of the eye: aso, orbits; 
DB, eye-ball ; r, optic nerve ; ¢ u, levator palpebre ; x, superior rectus; 
k, superior oblique muscles; 1, pulley of do.; m N, external rectus, cut 
through ; 0, inferior rectus ; @ to m, branches to the facial vein; op, oph- 
thalmic vein; gr s, ophthalmic branch of the facial vein; ¢t, vein from the 
superior rectus; wu, superior ciliary vein; vv ww, lachrymal gland vein; 
x, posterior nasal vein ; yy, veins from the sheath of the optic nerve. 
B. The Eye-Bail. 
The ball or globe of the eye, or the eye proper, is placed at the anterior 
and internal part of the orbit, behind the conjunctiva, surrounded by fascia, 
muscles, vessels, nerves, and adipose substance, and retained in its situation 
by the optic nerve, the recti and superior oblique muscles, which support 
or suspend it in the surrounding fat, and admit of its free and easy motions. 
It is small in comparison with the cavity which contains it. In some per- 
sons it appears more prominent than in others; the variety in this respect 
depends partly on the amount of adeps in the orbit, and partly on the size 
of the palpebral opening; it is also absolutely larger in some than in 
others. The eye is nearly spherical, and about one inch in diameter, but, 
in consequence of the slight projection of the cornea, which is a segment of 
a smaller sphere superadded to the larger one formed by the sclerotic, the 
antero-posterior axis is one or two lines longer than the transverse. A 
transverse section, dividing it into an upper and lower half, or a vertical 
section, dividing it into a right and left portion, will exhibit an oval outline; 
but a perpendicular section, cutting it into an anterior and posterior half, 
will exhibit the circular form. The long axes of the eyes are nearly parallel 
to each other, and therefore not so to that of each orbit. The eye is a hol- 
low globe, the wall or shell of which is composed of different membranes or 
tunics, and the cavity is filled by transparent fluids or humors for optical 
purposes. The coats are three, the sclerotic, the choroid, and the retina; 
these fit accurately one within the other, and are in close apposition. The 
first is called sclerotic; it is a fibrous membrane, for the protection and 
maintenance of the form of the organ; it invests the posterior four fifths, 
and presents a circular opening in front, into which the transparent cornea 
is inserted, which completes the anterior fifth ; the cornea and fore part of 
the sclerotic are also covered by the conjunctiva. Within the sclerotic is 
the second tunic, the choroid, which is extremely vascular, and contains the 
nutrient vessels and nerves; it also secretes the brown or black pigment, 
which deeply stains the interior of the globe and the back of the iris, to 
prevent the reflection of the rays of light from the bottom and sides of the 
organ back again through the retina. In the anterior part of this tunic there 
is also a circular opening or deficiency, into which the iris is fitted, as the 
cornea is into the sclerotic. External to the circumference of the iris the 
choroid is intimately attached to the sclerotic by the ciliary band or liga- 
ment; and internally and behind the iris it is connected to the membrane 
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