Eyes and nose. Coloured historical illustration of a cross-section through the human eyes and nose. Front is at top. A non-sectioned eye (upper right) shows the transparent cornea (front of eye) that refracts the light entering the eye. The lens (a disc-shaped object seen in the sectioned eye at upper left) lies behind the cornea, focusing light onto the light-sensitive retina inside the eye. The resulting nerve impulses are transmitted to the brain via the optic nerves, which run from the back of the eyes and cross at the chiasma (lower centre). The air-filled spaces of the paranasal sinuses are seen between the eyes. From Bilder Atlas by Johann Georg Heck, 1860.