The refraction of the rays of light in the eye is much more complicated than in a simple convex lens; for, in the eye, the ray of light passes through several substances, and is refracted at the surface of each substance. The common result, however, produced by all these refracting media of the eye is exactly the eye in a somewhat slanting direction with the side of the nose, pierces the sclerotic coat and choroid, and then spreads out on all sides, so as to form, by means of the peculiar terminations with which it is provided, a kind of nerve-carpet, which is the most delicate sensory organ created by nature. The retina, towards the front of the eye, touches with the outer 20
circumference of the iris, and lies quite open to the transparent interior of the eye, so that the rays of light fall directly upon it, and create in it an impression of light. Before, however, the rays of light reach the retina, they pass through a number of transparent organizations which are situated in the circular hollow of the eye, and are here ingeniously fitted together like the parts of a microscope or telescope, with this difference only, that they are packed tightly together, so as to allow no trace of air between them. The outer covering of this transparent body is the cornea, mentioned above; then, towards the interior, follows first the aqueous humour, secondly the crystallize lens, L; and thirdly, the vitreous The aqueous humour fills, as we have seen, the space between the cornea, the iris and the lens. Directly behind the iris lies the crystalline lens, so well known, and resembling a very thick burning-glass. It is more convex upon its posterior than upon its anterior surface; in a living eye it is as clear-as crystal, and consists of a somewhat soft substance, which becomes harder towards the back of the lens. It has been discovered that this substance is not the same throughout, but that it consists of small vessels which are arranged in intricate lines, thus giving a sex-radiated structure to the lens.
SENSING SURVIVAL
NOTICE
OB S ERVATION
OB S ERVE
WATCHING
WATCH
S IG HT
VIEW
S EEING
S EE
ENVIS AG E
D IS COVER
P ROJECT
CHECK
LOOK
U ND ERS TA ND
VIS UA LIZE
REA LIZE
ANATOMY OF THE EYE