(M264) The ancient Egyptians like the Aztecs considered a year to consist of three hundred and sixty ordinary days divided into months and eked out with five supplementary days so as to bring the total number of days in the year up to three hundred and sixty-five; but whereas the Aztecs divided the three hundred and sixty ordinary days into eighteen arbitrary divisions or months of twenty days each, the Egyptians, keeping much closer to the natural periods marked by the phases of the moon, divided these days into twelve months of thirty days each.(778) This mode of regulating the calendar appears to be exceedingly ancient in Egypt and may even date from the prehistoric period; for the five days over and above the year (_haru duaït hiru ronpit_) are expressly mentioned in the texts of the pyramids.(779) The myth told to explain their origin was as follows. Once on a time the earth-god Keb lay secretly with the sky-goddess Nut, and the sun-god Ra in his anger cursed the goddess, saying that she should give birth to her offspring neither in any month nor in any year. He thought, no doubt, by this imprecation to prevent her from bringing forth the fruit of her womb. But he was outwitted by the wily Thoth, who engaged the goddess of the moon in a game of draughts and having won the game took as a forfeit from her the seventieth part of every day in the year, and out of the fractions thus abstracted he made up five new days, which he added to the old year of three hundred and sixty days. As these days formed no part either of a month or of a year, the goddess Nut might be delivered in them without rendering the sun-god’s curse void and of no effect. Accordingly she bore Osiris on the first of the days, Horus on the second, Set or Typhon on the third, Isis on the fourth, and Nephthys on the fifth. Of these five supplementary or intercalary days the third, as the birthday of the evil deity Set or Typhon, was deemed unlucky, and the Egyptian kings neither transacted business on it nor attended to their persons till nightfall.(780) Thus it appears that the ancient Egyptians regarded the five supplementary or intercalary days as belonging neither to a month nor to a year, but as standing outside of both and forming an extraordinary period quite apart and distinct from the ordinary course of time. It is probable, though we cannot prove it, that in all countries intercalary days or months have been so considered by the primitive astronomers who first observed the discrepancy between solar and lunar time and attempted to reconcile it by the expedient of intercalation.