Congenital atresia of the genital canal may occur in any part of its course. Imperforate hymen is the most frequent as it is the least dangerous form, being more than twice as common as atresia of the vagina and three times as frequent as that of the cervix uteri. The vagina may be extremely small in calibre, closed in part or the whole of its course, or only a fibrous cord indicate where it should be. The uterus may be closed at the internal or external os; the latter is the more frequent. An occlusion at one point does not preclude the existence of other closures higher up. The effect of a closed canal with a recurring secretion above is evident, and gives rise to a well-marked class of cases. The organs above become distended, and the distension increases until an opening is made by art or the retained fluid bursts a passage for escape. This may occur outwardly with immediate relief and cure, or into the peritoneal cavity, causing speedy death. The time at which the uterus may be expected to give way under such distension cannot be stated, as the power of resistance of the organ differs and the amount of secretion each month may vary widely. Scanzoni in one case evacuated eight pounds of blood, the result of seven months' accumulation, and found the uterine wall as thin as paper. Bernutz states that the average time before interference is necessary is three or four years, and gives a case first operated upon in the tenth year of its course. Menstrual retention is not at first indicated by pronounced symptoms. Suspicion of the nature of the case may be first excited by the severity of those symptoms which at every period announce the approach of menstruation and known as the menstrual molimen. As distension increases these become extreme, with rectal and vesical tenesmus and severe uterine colic. The nervous system sympathizes, as with all menstrual derangements, and there may be rigor, fainting, or even convulsions.