The reconstruction of the list of the 20 days in the ritual calendar and their Mixtec names was made possible by the studies of the codices of the northeastern area of Oaxaca done by Caso (1958), Jiménez Moreno (1962), Dahlgren (1952), and Smith (1973).Their works have truly been the key for relating the logograms, the numerals, and the days to their corresponding Mixtec word. This paper shows how three codices from the Mixteca Baja —Mapa de Xochitepec, Códice Mixteco Postcortesiano no. 36, and the Mapa de San Vicente el Palmar— mention the calendrical names of the rulers, whose anthroponyms transcriptions were formerely unknown. The glosses in Mixtec in these documents allow us to corroborate the Mixtec names of the days in most positions, with slight variations in their graphic symbols, and the use of a special language for Mixtec names.