ORIFICE OF THE VAGINA, AND HYMEN.—. Immediately below the vestibule, and between the nymphw, is the orifice of the vagina (fig. 480. v a), which, in its undistended state, has the form of a vertical fissure, especially in women who have borne children, but in virgins it is more constricted and circular, and is further narrowed by a fold of the vaginal mu cous membrane, the hymen, which either en circles or semi-encircles the orifice. As some important questions in obstetric and forensic medicine relate to this membrane it will receive here a more particular examination.
The hymen, regarded in an anatomical point of view, possesses no peculiarity or speciality by which it is essentially distinguished from many like structures in other parts. It belongs to the same class of formations as the valvulw conniventes of the intestines, and the frill-like folds of mucous membrane which not infre quently surround the terminal orifices of mu cous tubes. In the fcetus such folds are seen with various degrees of distinctness at the ter mination of the urethra, vagina, and often of the rectum. The lower end of the vagina, in the fcetus invariably terminates in a marked projection outwards of the mucous lining of the tube. It takes the form of a laterally compressed conical fold, the base of which is continuous all round with the vaginal walls, but the apex is directed forwards. Its centre exhibits a vertical slit-like orifice, the direction of which is apparently due to the lateral com pression of the nymphw and labia, between which it lies. This is the hymen. In ad vanced fcetuses it is scarcely distinguishable in form, and only to a certain extent in size, from the similar conical termination of the cervix uteri, which projects into the vagina, as the hymen does between the nymphw. The vaginal portion of the cervix uteri and the hymen both constitute invaginations or intussusceptions at two different points of the same mucous tube, —the one 'narking the division between the uterus and the vagina, the.pther between the latter and the external parts. The chief dif ference between them is that the direction of the orifice in the former is transverse, and in the latter vertical.
Such is the condition of the hymen during• fcetal and infantile life. But as growth advances the posterior half becomes much more developed than the anterior, just as the posterior half of the uterus, the poste rior lip of the cervix, and the posterior wall of the vagina, are commonly larger and more developed than the corresponding anterior halves. Thus it happens that in adults the
hymen presents usual ly the form of a crescentic or semilunar fold, the concave border of which is directed upwards or forwards, while that which had been in the fcetus, the upper half, has now become unfolded or lost among the plaits of mucous membrane, situated at the upper part of the vaginal entrance. This, because it is the most constant, has been usually regarded as the typical form of the hymen. But the fcetal form is also often re tained, namely, the circular fold of mucous membrane, which, as the parts become more expanded, acquires a round rather than a slit like aperture. If, however, the folds of the mucous membrtme lining the vagina are pro fusely developed, then the hy men also exhi bits the form not so much of a distinct membrane as of an irregularly constricted ori fice, the sides of which are puckered or gathered into plaits, so as nearly to close the vaginal entrance. And this also is a very common condition of the part, especially in young subjects.
The varieties, therefore, in the hymen which anatomists recognise, such as the crescentic, circular, cribriform, and the like, become easily explicable. They all proceed apparently from a common starting point, but differences in the degree of development, or accident, may determine the permanent form. The half: circle and crescent result from a normal deve lopment of the posterior, and a corresponding retrocession of the anterior, moiety of that conically projecting mucous fold which is more or less distinct in every fcetus. The hymen with a central or nearly central circu lar orifice, results from a flattening down and retiring within the vaginal orifice of the cone ; the retiring naturally following upon an expan sion of the vaginal walls as growth advances. The appearance of a notched margin to the cen tral aperture is produced by the prominent edges of the terminal vaginal folds, which are in some subjects more profusely developed than in others. The cribnform hymen pro bably results from an abnormal cohesion of these notched edges, in such a manner, that small apertures are left between them, and the completely imperforate hymen by- an en tire adhesion of the margins of the orifice, the result sometimes of inflammation in in fancy.