The second maqāla begins with a synthetic presentation of the three “schools of thought” ( maḏāhib ) on the theories of vision. As far as the first school is concerned, a number of scholars loosely relating to extramissionism are mentioned and their optical theories addressed. Euclid has a preeminent role in this group. The description of his geometrical optics – by means of mathematical demonstrations integrated by diagrams – occupies two-thirds of the entire maqāla (see below, Section 2). The first school is in fact labeled as the school of “mathematicians” ( al-riyāḍiyyīn ), that is, the proponents of Euclidean geometrical optics, according to a definition introduced by Alexander of Aphrodisias (2nd c.) ( Jones 1994 , 47). 1 As for the textual source for this passage, the contents are excerpted verbatim from the Placita philosophorum by Ps.-Plutarch ( Plutarch 2017 , 900B-C) in its Arabic version. 2 According to Daiber, the quotation in NU is probably mediated through the al-Rawḍa al-ṭibbiyya (“The Medical Garden”) authored by ʿUbayd Allāh b. Ǧibrāʾīl b. Bukhtīšūʿ (5th/11th c.) ( Daiber 1980 , 84), which is in fact mentioned three times in NU (Ṣalāḥ al-Dīn b. Yūsuf al-Kaḥḥāl al-Ḥamawī 1987 , 240, 251, 416). 3