The _pelvic floor_ is not a simple structure but a complicated arrangement of organs and tissues. If we begin to examine it from below upwards, we first have its outer covering in the skin; then, the superficial and deep fascias, the triangular ligament of the bladder and a group of interlacing muscles. The organs that enter into the composition of the pelvic floor and interwoven with the preceding structures, are the bladder, the vaginal walls, the rectum and connective tissue. Examine Plate II. Through this floor there are several openings, which are guarded by a special set of constrictor muscles that are termed _sphincters_. These are sufficiently strong in the bladder and rectum but in the vagina they would be entirely insufficient to close this canal effectually. The vagina, or, for our purpose, it will be clearer if we say “_vaginal canal_,” divides the pelvic floor into an anterior and posterior segment, and it is by means of this division that the whole structure of the pelvic floor is weakened; this will be perceived at a moment’s reflection, when we compare it with the pelvic floor of the _male_, who has no vagina; and for this reason men are never troubled with the _prolapses_ to which women are liable. Nature, however, has made an attempt to compensate this physical defect in a manner that reduces the weakness occasioned by the vaginal canal to its minimum. The vaginal canal does not enter the pelvic cavity in a directly upward or perpendicular course, but obliquely upwards and backwards, as may be seen by referring to Plate II. The result is that the intra-abdominal pressure falls on the vaginal walls from above, and thus compresses and approximates the anterior and posterior walls of the vagina to each other, so that it constitutes a self-closing valve, but, notwithstanding all these provisions, this slit or opening through the pelvic floor still remains the weakest point of the inclosure for the pelvic and abdominal viscera. When the causes are sought that underlie the various displacements of the uterus, they are generally to be found in an impairment of the pelvic floor, through some changes or accidents that are peculiar to pregnancy and delivery.