The important part of the operation for this injury consists in the repair of the muscle. In many operations the recto-vaginal septum is repaired and the cutaneous portion of the perineum is repaired, but the operator fails to secure in his sutures the sphincter ani muscle, and consequently the incontinence is not cured (see Fig. 36). The mistake often made is that the sutures that are introduced to close the anterior margin of the anus are inserted too far forward and too far out to catch the ends of the sphincter ani muscle, which has retracted so that, in some cases, it lies altogether behind the anal opening. Or, perhaps, only the outer fibers of the sphincter ani are included in the suture, and partial incontinence results. [Illustration: FIG. 36.--Imperfect repair of the sphincter ani. The muscle has not been included by the sutures, and does not surround the anal opening.] The position of the sphincter ani muscle is indicated by the corrugated or wrinkled skin overlying it. The ends of the muscles, being retracted, do not lie in the plane of the laceration, but their position is marked by a depression or dimple (Fig. 37). The technique of the primary operation is included in a consideration of that of the secondary operation, the only difference being that in the latter operation denudation is necessary. The parts should first be denuded, so that they present the same raw surface that was exposed in the original laceration. The lower end of the recto-vaginal septum that forms the anterior margin of the anal opening is usually thin and cicatricial where the mucous membranes of the vagina and rectum unite. All this cicatricial tissue should be cut away, and the mucous membrane of the vagina may be drawn forward and separated by dissection from the mucous membrane of the rectum, in order to make a somewhat broader surface through which to pass the sutures. Special care should be directed to the denudation of the ends of the sphincter muscle. The tissue lying at the bottom of the depression that marks the end of the sphincter should be picked up with forceps or a tenaculum and carefully cut away. In removing tissue attached to the mucous membrane of the rectum the operator should avoid cutting the healthy portion of this mucous membrane, as bleeding from it is often annoying. [Illustration: FIG. 37.--An old laceration through the sphincter ani. The sphincter muscle lies behind the anal opening. Its position is indicated by the wrinkled skin; its ends are marked by the depressions on each side of the anal opening.]