Fig. 20.—Dissection of female perineum, showing the deeper structures after removal of the levator and sphincter ani muscles.
The vagina has no circular sphincter like the anus, but the vaginal month is kept closed by the action of the transversus perinæi, sphincter vaginæ, and levator ani muscles, which draw the perineum forward, and thus keep the posterior vaginal wall in apposition with the anterior wall.
Fig. 21.—Muscular floor of the pelvis seen from above.
This sling of muscles and fascia, which surrounds and supports the opening of the vagina, may readily be felt in the nulliparous woman by introducing the finger in the vagina and pressing backward and outward toward the ischio-rectal fossa. We then feel plainly, immediately within the ostium vaginæ, a firm resisting band of tissue, apparently about half an inch broad, embracing the posterior portion of the lower vagina. This band is formed by the inner edges of the various muscles and planes of fascia that have been described.
Fig. 22.—Sagittal section showing relations of the several layers of fascia within the pelvic floor (Dickinson).
The vagina extends, as a transverse slit in the pelvic floor, upward and backward, approximately in the direction of a line drawn from the ostium vaginæ to the fifth sacral vertebra. It is approximately parallel with the conjugate of the brim, so that when the woman is erect the long axis of the vagina is inclined at an angle of 60° to the horizon. The vagina is not a vertical open tube: it is a slit in the pelvic floor, in health always closed by the accurate apposition of the anterior and posterior walls ([Fig. 21]). The anterior vaginal wall is about 2½ inches long in a vertical mesial line. The posterior vaginal wall is about 3½ inches long. The vaginal walls are triangular in shape, being broader above than below. The shape of the normal vagina at the pelvic outlet is shown by [Fig. 23]. The section here shows the vaginal slit of the shape of the letter H. The portions of the slit extending backward and somewhat outward are called the vaginal sulci or furrows. They are directions of diminished resistance in which tears are liable to occur.
Fig. 23.—Section illustrating the characteristic form of the vaginal cleft (Henle): Ua, urethra; Va, vagina; L, levator ani; R, rectum.]