IV. Traction from below may be due to vaginal cicatrices, abnormally short vagina, falling of the pelvic floor, etc. Obviously, descent of the vesico- and recto-vaginal walls, or, more comprehensively, the sacral and pubic segments of the pelvic floor, involves also concurrent descent of the uterus. Descent of the vagina, therefore, must be studied in connection with the descent of the uterus. Excessive descent of the vaginal walls usually originates with parturition. In labor the anterior wall of the vagina is so depressed, stretched, and shortened by the advancing head that during and after the second stage the anterior lip of the cervix may be seen behind the urethra. If the puerperium progress favorably, with prompt involution of the uterus, vagina, perineum, and peritoneum, the relaxation of the vesico-vaginal wall and of the utero-sacral supports disappears and the uterus resumes its normal multiparous location and position.[7] But if the enlarged uterus remain in the long axis of the vagina, with its fundus incarcerated in the hollow of the sacrum between the utero-sacral ligaments, and with its sacral supports so stretched that they cannot recover their contractile power, and with involution of all the pelvic organs arrested, the descent {155} may not only persist, but may even progress with constantly increasing cystocele to the third degree of prolapse. The downward influence of the above conditions may be materially increased by rupture of the perineum, and consequent prolapse of the recto-vaginal wall into a pouch called rectocele. [Footnote 7: The anteflexion of the multiparous uterus is less than that of the virgin.] In the great majority of cases of complete prolapse the posterior vaginal wall in its descent is peeled off from the rectum, leaving the latter in its normal position. In rare instances the lower portion of the rectum is also found to have extruded in extreme rectocele, making a pouch below and in front of the anus, where fecal matter may accumulate and remain in hard scybalæ. Obviously, complete prolapse of the uterus is only an incident to the prolapse of the pelvic floor. The whole mechanism is in all respects analogous to that of hernia. The extruded mass drags after it a peritoneal sac, which, hernia-like, contains small intestine. This sac forces its way to the pelvic outlet and extrudes through the vulva, having the inverted vagina for its covering. [Illustration: FIG. 3. First Degree of Prolapse of the Post-partum Uterus. The posterior vaginal wall has been changed from its normal forward direction to a vertical direction by perineal rupture and anterior displacement of the cervix; the vesico-vaginal wall descends in cystocele, becomes hypertrophied, and drags the heavy uterus after it. The descending uterus carries with it a reduplication of the vaginal walls.]