168 ANTHROPOLOGY. 



/ branch to the inferior oblique muscle ; // stronger branch to the external 

 rectus muscle ; g h i, separation of the lachrymal artery, and to the lachry- 

 mal gland and upper eye-lid. Fzg. 16, veins of the eye: a B c, orbits; 

 D E, eye-ball; F, optic nerve; G H, levator palpebrae ; k, superior rectus; 

 k^ superior oblique muscles; l, pulley of do.; M N, external rectus, cut 

 through ; o, inferior rectus ; a to m, branches to the facial vein ; o p, oph- 

 thalmic vein ; q r s, ophthalmic branch of the facial vein ; 1 1, vein from the 

 superior rectus ; u u, superior ciliary vein ; www, lachrymal gland vein ; 

 X, posterior nasal vein ; 3/y, veins from the sheath of the optic nerve. 



B. The Eye-Ball. 

 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 arc nearly parallel 

 to each other, and therefore not so to that of each orbit. The eye is a hol- 

 low globe, the Avail 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 coeds 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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