(d.) The blood is supposed to escape by permanent vascular orifices.
In the present state of our knowledge, the evidence in support of this view is not more conclusive than that upon which the preceding hypothesis is built : yet many circumstances lend colour to it. The question of a termina tion of the uterine vessels by open orifices has been occasionally, though obscurely, touched upon by different authors. Thus, Madanrie Boivin t, a most careful observer, after speak ing of the " perspiratory orifices of extreme minuteness," visible upon the inner uterine surface, evidently meaning the orifices of the now well-known uterine glands, describes the manner in which the blood may be made, by pressure, to appear in droplets upon the inner surface of the uterus when death has occurred during menstruation ; and,without giving a per sonal opinion, she elsewhere quotes the then prevailing views, that the blood is furnished by the exhalent extremities of arteries termi nating upon the inner surface of the uterus. Dr. Sharpey § endeavoured, by various ex pedients, to determine what is the precise re lation of the blood-vessels to these orifices in the decidua a little more advanced*, as, for example, in early pregnancy ; but after express ing his conviction upon the subject, the pre cise anatomical connection between the two is left undetermined. Ordinarily, in injecting the uterus with fine coloured fluids, I have ob served the cavity to become filled, the injec tion apparently escaping by the glandular ori fices, which also themselves may be seen filled with injection. In some specimens a capillary branch may be observed passing to and stop ping short at one of these canals or orifices, and having much the appearance of an open vessel. Without personally expressing an opinion upon this point until I have carried further some experiments now in progress, I may observe, that the idea of a permanently open termination of vessels here need not be set aside upon the objection that such an ar rangement would produce a constant bleeding, because the vessels supplying the blood must first pass through a dense muscular tissue, amply sufficient to control or arrest bleeding, as indeed it does effectually after labour, when much larger mouths are laid open, and also occasionally when menstruation is suddenly arrested by powerful mental impressions, acting apparently upon the muscular fibre of the uterus ; while many positive facts might be adduced in support of such a view, such as the frequent bleedings of uterine polypi, which are always invested by mucous membrane, the ready passage of fluids through the surface of the latter when their main vessels are injected, and the like.
What is the purpose of To this question no reply will be satisfactory which does not include the consideration of many other circumstances besides the mere escape of blood. Menstruation has evidently a much deeper signification than is declared simply by the flux, which is probably not the most important part of the function, although it constitutes the external sign or evidence of it.
Amid all the crude hypotheses of former times, such as that menstruation is due to fer mentation, lunar influence, and the like, some of the older writers appear nevertheless to have had a dim perception of the truth when, under the form of an elegant type, they shadowed forth that which appears to be the real pur pose of the menstrual act. The French term, "fleurs," and the English, " flowers," are now fallen into disuse ; but they were employed in earlier times as designations of menstruation, for the purpose of suggesting that, after the example of trees, which do not bear unless the fruit is preceded by the blossom, so a woman .does not become pregnant until she also has had her flowers.t Menstruation is not established until the ovaries have reached a certain stage of de velopment, and the maturation and discharge of ova has commenced.* It continues to be performed as long as the process of ovulation is continued ; but when the latter ceases, and the ovaries have become shrunken, their tissues attenuated and wasted, and Graafian follicles can be no longer distinguished, menstruation ceases to be performed.