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. [Illustration: FIG. 23.--Section illustrating the characteristic form of the vaginal cleft (Henle): _Ua_, urethra; _Va_, vagina; _L_, levator ani; _R_, rectum.] CHAPTER VI. INJURIES TO THE PERINEUM. The injuries to the perineum that may result from childbirth are classified according to the position or the direction and extent of the laceration. They are as follows: slight median tear; median tear involving the sphincter ani; tear in one or both of the vaginal sulci; subcutaneous laceration of the muscles and fascia. All these injuries demand operative treatment. The operation for the repair of injuries to the perineum is called perineorrhaphy. It is called immediate or primary, intermediate, and secondary perineorrhaphy, according to the time after the receipt of the injury at which the operation is performed. The primary operation is done during the first twenty-four hours. The primary operation should always be performed. A careful inspection of the perineum and the posterior vaginal wall should always be made after labor, and any laceration should be repaired within twenty-four hours. The advantages of the primary operation are many. The parts are usually so numb that it is not necessary to administer an anesthetic. No denudation is necessary, and therefore no tissue need be sacrificed. The woman is spared the pain and discomfort of granulation and cicatrization.