right now at this very moment as you watch these light rays striking the magnified by similar tiny beams of light are entering your own eyes and it's by my eyes that we are able to gain a great part of our knowledge nature has located eye close to the brain so that its messages may arrive there quickly nature is also provided ample protection for this very delicate organ here with the outer covering is removed we see the eyeball completely surrounded by clearly once again we see the fetid cushion which protected on all sides know this white stalk which is the optic nerve and also these muscles which move the eyeball this is the empty i suck at within the skull with its bony walls inside and the rim of the bony or butt in front by gradually restoring the outer portions of the skull and also the covering tissues we can now realize the location of the entire in relation to the outline of the face another important safeguard to the eye is the tear gland which secretes the tear fluid this is an effective germicide which drains through the tear ducts into the nose after flushing and cleaning the entire i s the eyeball itself has a white glistening surface its front part bulges and forms a highly transparent window in this sectional view the capstone of the eyeball the seem to have three layers t outer layer is called the sclera and serves to protect the delicate structures within this transparent bulging portion is called the cornea notice also the presta lens which is one of the main features of the the second layer is called the choroid it consists of three different belts or zones the first stone is called the choroid proper and is the part that carries nourishment to the tissues of the the third zone is the well known iris which expands and contracts the people much like the diaphragm of the camera the iris will soon be described in greater detail magnified many hundred times the retina is seen to consist of this complicated arrangement of rods and cones which convert light waves into nerve impulses in some manner which even science of today cannot fully explain now just how do the light rays active form a clear picture within the eye first let us realize that light rays reflected from any object radiate in all directions and that as an object moves farther away from us the angle between the rays that enter our eyes grows smaller and smaller and finally when the object is reached a distance of fifteen feet or more the ray is entering our eyes are practically parallel but if a distant object approaches the eye the angle between entering rays again grows larger this increasing angle changes the direction of the light rays as they pass through the lens so that the sharp image falls behind the right as a result the image upon the retina tends to become blurred this blurring causes a response or reflects within our brain which brings about our money as internal adjustments  all parts of the eye that are just one is called accommodation accommodation restores the sharply focused image with marvelous speed and accuracy this is all the more remarkable because the distance between retina is fixed and the lens itself must change its shape now compare this with the focal adjustment of a camera here the lens remains unchanged but the film itself is moved until it reaches a sharp is also necessary that both our eyes be fixed upon the same point in order that we may see an object clearly us as an object approaches us from a distance or eyeballs turn accordingly this movement is called the convergence of visual axes this action is shown here as the object approaches and recei addition we see the lenses accommodating their optical shape under the combined influence of blurred image and eyeball movement golick which cannot be compressed you may ask then how is the soft pliable body of the limbs made to take on the different degrees of convexity necessary for accommodation in order to explain this that is again call attention to the important ciliary muscles which we see here in the diagram this muscle is shaped like a broad ring which going to expand and contract whenever it does contract it was confining quantity so the only part which can possibly yield to the pressure of the vitreous humor or body is the soft substance of the limbs so whenever the image upon the retina becomes blurred the brain automatically causes the ciliary muscles to contract or to relax until the lens is attained just the right shape to restore a sharply defined image upon the retina as a result of these distortions the purple now contracts don't they die if you israelis have been shut away and only a clear image remains upon the retina these interesting mechanics of the lens are not generally known in the facts presented here i've only recently been accepted by science it is well first and know that our eyes are one of our greatest gifts of nature and are indeed were they about our constant care and protection