UNPUBLISHED SHEETS OF LEONARDO DA VINCI

NERVES AND VESSELS

The entire space of the air that faces the eye is filled with infinite images original: "similitudini"; these are the "visual species" or likenesses of objects that Leonardo believed traveled through the air of the things placed in that air, all of which intersect through the pupil of said eye within that pupil. Thus, the forms of said air are all reduced into said pupil as if into a single point, and from said point they expand through the crystalline humor the lens of the eye and strike the surface of the spherical humor the vitreous humor and then pass to the common sense term: "senso comune"; the central faculty of the brain where all senses were thought to meet and be processed.

But here a doubt arises, and it is this: that if these images wish to penetrate through the pupil as far as the common sense—which said images intersect in said pupil—it follows that the images of things placed on the right would go to the left, and those on the left to the right. And likewise, the form of a man who stands upright would go to the common sense upside down. Therefore, reason teaches us that by necessity of said intersection, these images must be re-inverted original: "risvolgere"; to turn back or flip again, and this must be done by the concavity of the crystalline humor, which by its spherical shape re-inverts said images. And this reasoning shall be proven in its proper places with experience and with demonstrations.