According to _Westphalen_, whose investigations were made, partly on masses removed by the curette, and partly on freshly extirpated uteri, a sanguineo-serous infiltration of the mucous membrane begins about ten days before menstruation. Great vascular dilatation occurs only just before menstruation. The uterine glands undergo enlargement, and during and immediately after the flow, numerous shed epithelium cells occupy the lumen of the glands. For the rest, however, in the interior of the uterus shortly after menstruation, we find an almost continuous epithelial covering. Some days after menstruation, the proper regeneration of the mucous membrane occurs. _Mandl_, who examined totally extirpated uteri, asserts that during menstruation the epithelial covering of the mucous membrane is never completely lost, but that just as little does it remain completely intact. The regeneration of the lost areas of epithelium proceeds even during menstruation. The researches of _Kundrat_ and _Engelmann_ on uteri obtained post mortem led these authors to describe as follows the anatomical changes that occur in the uterine mucous membrane at the time of the catamenial hæmorrhage. In the premenstrual epoch a round-cell infiltration occurs in the interglandular tissue, the lumina of the uterine glands become enlarged, and the bloodvessels dilated; subsequently, fatty degeneration of the superficial epithelium and the epithelium of the glands occurs, leading to laceration of the vessels and destruction of the affected area of tissue; after the cessation of the bleeding, regeneration of the mucous membrane occurs.