The Orlando Innamorato in English translation, Book I, Canto VIII, Stanzas 41-64 Notes.
46. Boiardo is airing his classical learning here. (He translated several Greek and Latin classics into Italian) Just as the vengeance of Marchino’s wife is based on the Greek myth of Procne and Philomela (which Boiardo would have read in Ovid), so Marchino’s vengeance was the favorite punishment of King Mezentius in the Aeneid.
50. Boiardo now moves from classical lore to medieval, as is typical of him. A similar story to this one was brought back by the Crusaders from the Byzantine Empire. It was a development of the Gorgon legend, and told how a young man who lived near the Gulf of Satalia [now called Antalya], consumed with lust for his deceased lady-love, begot a terrible head that, every seven years, rose out of the Gulf and brought misfortune or storms. Various versions can be found in Walter Map’s Courtiers’ Trifles, Book 4; Gervase of Tilbury’s Otia Imperialia 2.12; Mandeville’s Travels, usually near the section on Constantinople; and other places.
52. The cruelty is partly gratuitous, but partly prudent: it keeps prisoners from escaping and from needing to be fed.
57. Turning horns are generally attributed to the eale or yale, a creature found in Pliny (VIII.30) and sometimes in heraldry, but not, as far as I have ever seen, appearing in fiction or folklore.