hA2 ANTHROPOLOGY. 
membrane or capsule. It differs but little from water in specific gravity 
and refractive power. Chemically it consists of about ninety-eight parts 
of water and two of chloride of sodium, with a trace of albumen. The 
space occupied by this humor is divided into two apartments by the iris, 
anterior and posterior. 
8. Tue Crystatiine Lens is a transparent, double convgx lens, the 
anterior convexity less than the posterior. The former forms part of a 
circle whose diameter is seven or eight lines in length, the latter one of 
four or five lines. Its convexity varies, however, with age. A perfectly 
transparent elastic capsule invests the lens proper. On opening the ante- 
rior part of the capsule of an eye long dead, a liquid escapes, known as 
liquor Morgagnii. This accumulation of liquid in all probability does not 
exist in the recent eye. The crystalline lens itself is of quite complicated 
structure. When boiled it can be separated into concentric layers, of 
which the exterior are soft, the internal increasing in hardness to the 
central nucleus. These lamine appear to consist of parallel fibres united 
by finely serrated or toothed margins. During the separation of these 
lamineze, a moderate pressure will cause the whole to part into three 
triangular or wedge-shaped segments. In the recent lens, the density of 
the layers increases from the surface towards the centre, this involving a 
corresponding increase in refracting power. Consequently, rays of light 
falling on the exterior of the lens, will be refracted to the same focus as 
those passing through the centre meeting there a more highly refracting 
medium. Certain defects of vision depend greatly on abnormalities of the 
crystalline lens. Thus a convexity greater than usual produces short-sight- 
edness by causing the rays of light to converge to a focus in front of the 
retina, thus necessitating an unusual approximation of an object to the eye. 
In long-sightedness, the lens being less convex than usual, the rays tend to 
a focus behind the retina, and to bring this point of convergence on the 
retina, the object has to be held at a greater distance. 
9. Ture Vitreous Humor, or tue Hyatomw Bopy, fills the posterior three 
fourths of the globe, and is in contact with the whole of the inner surface 
of the retina. Anteriorly and centrally the crystalline lens is imbedded in 
it, and more externally the ciliary processes are attached to it. In the 
adult it is perfectly transparent, and consists of a membranous capsule and 
areolar tissue secreting and inclosing a fluid like water. The hyaloid 
membrane or capsule not only incloses the humor, but sends inwards 
numerous processes, which join each other, and form a fine areolar or 
cellular tissue, in the interstices of which the fluid is confined. These cells 
all communicate with each other, as a single puncture will permit the 
gradual discharge of all the fluid. The vitreous body is traversed by a 
small artery from the centralis retin, extending to the capsule of the lens. 
The vascular layer of the retina also in all probability sends into it vessels 
and nerves. 
From the preceding description it must appear that the eye is not 
only of complete structure and delicate organization, but is also a refined 
optical instrument. The rays of light proceeding from any object strike 
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