ae esa ease Crystalline Lens in Man. 129 
the lens is less flattened than in adult man, resembling more nearly 
the shape of the human fcetal lens. 
The lens of vertebrate animals is formed almost entirely of a 
peculiar fibrous tissue, with a very scanty formless interstitial sub- 
stance. It is enclosed in a shut capsule, the integrity of which is 
of the highest importance to its transparence. This capsule is a 
perfectly transparent, very elastic yet brittle, membrane. It is 
little prone to degenerative metamorphosis and never undergoes 
absorption. I have found it transparent and unchanged sixteen 
years after the extraction of the lens for cataract. Its chemical 
constitution and reactions resemble those of the other hyaloid mem- 
branes, it is unaffected by weak acids and alkalies, and it resists 
putrefaction. With high magnifying powers no indications of 
structure are discernible in it, except faint marks of lamination in 
the stout capsules of the large mammalia. The front half of the 
capsule, or more exactly that part of it which lies in front of the 
attachment of the suspensory ligament, is thicker than the posterior 
half; at a rough estimate its thickness may be taken to be three 
times as great. 
This difference and the unavoidable implication of the front 
half of the capsule in operations for the removal of cataract, have 
led to the adoption of the terms anterior and posterior capsule. 
As these terms are convenient, their use is not objectionable if it be 
borne in mind that they refer to two halves of one and the same 
sac, and not to two distinct sacs. 
Besides being stouter, the front half of the capsule differs also 
from the posterior, in being lined with an epithelium. This consists 
in the central region of a single layer of large, flat, polyhedral cells, 
each enclosing a circular nucleus. These nuclei are remarkably 
uniform in size and shape. At the edge of the lens the epithelial 
cells are much smaller, and so closely crowded that their nuclei are 
separated by very small interspaces. In mature lenses the marginal 
epithelium is composed of only a single layer of cells, but in young 
and growing lenses it is formed of several layers of cells, with an 
imbricated arrangement which constitute the matrix, out of which 
the fibrous tissue of the lens is evolved. 
The capsular epithelium plays an important role in the so-called 
capsular opacities accompanying various forms of cataract, con- 
genital as well as acquired, for out of it are evolved, by what may 
be called a perverted development, nucleated fibrous webs, often of 
great toughness and density, underlying the inner surface of the 
capsule. It must not be forgotten that the capsule itself never 
becomes opaque, what are called opacities of the capsules being 
always deposits of opaque substances and adventitious growths upon 
its surfaces. These may exceptionally be overlaid by a transparent 
colloid substance, and then an opacity may seem to be seated in the 
