DISTINCTIO II.

Having three chapters. The first is about the origin of the nerves which are extended to the eye.

These things being manifest, therefore, so that no scruple of doubt may occur in what follows, the composition of the eye must be considered, because without this nothing can be known about the mode of seeing. But certain authors say less, others more, and they are diversified in some things. For the authors of optics original: "perspectivæ" speak more generally about these, supposing [the knowledge of] natural philosophers and authors of medicine, as if everyone who reads the sciences of perspective has already foreseen [the works of] the physicians and naturalists. And therefore their discourse is obscure in itself, and is not understood unless one recurs to the fuller intention of the physicians and naturalists, for which reason it is necessary here to say something more amply than what is found among the writers of optics. And although it is too difficult to certify these things and to explain [what has been] certified, nevertheless I hope that these things can be made manifest through certain authors. But so that I do not needlessly lead off the streamlets of individual opinions, I will recite the composition of the eye principally according to three authors, namely Alharen Alhazen in the 1st [book] of Perspectiva, and Constantinus Constantine the African in the book On the Eye, and Avicenna in his books, for these suffice and discuss more certainly what we want; I cannot, however, follow the individual words of each one, because sometimes they contradict each other due to a bad translation, but from all of them I will form one truth. Therefore, all agree that there are two parts of the anterior concavity of the brain, which they call ventricles or concavities, or cells, and these ventricles cannot be the instruments of the common sense and the imagination, of which it was spoken before, for they