Theses de suppressis mensibus

...we decide thus: gradually, through the assiduous nutrition of the parts, some good and superfluous substance is collected. And if it has increased in its abundance so much that it begins to be a burden to the nature of the parts in the habit of the body: it directs it through the veins to the uterus, and subsequently, if no fetus is present, with the mouths of the vessels opened and unsealed, it is expelled.

XI.
It is expelled, however, through the vessels that are in the Uterus, namely through the veins; which, having arisen from the superior right and left emulgent renal veins, and joined with the inferior ones ascending from the groin from the vena cava and aorta, and disseminated through the substance of the uterus, serve the exportation of blood just as they serve its importation. There are also those who think it is ejaculated through the spermatic pores, into which anatomists have reported that the notable branches from the veins bringing nourishment terminate: besides the fact that through those which are in the female sinus, propagated from the Uterine Veins, the purging of pregnant women is sometimes seen to occur.

XII.
As the circuit and periodic movement of menstrual blood is certain, since the Menses observe their limit precisely with all things naturally administered and completed in the woman’s body, neither anticipating nor postponing: so too is its cause highly doubtful and controversial.

XIII.
But just as celestial bodies, especially the Sun and Moon, have a great power of altering and changing all natural things...