CHAPTER V.
ANATOMY AND MECHANISM OF THE PERINEUM.
An accurate knowledge of the anatomy and mechanism of the female perineum is essential to an understanding of the nature and treatment of injuries to this structure. The anatomical structures lying between the anus behind and the symphysis pubis in front are those that most directly interest the gynecologist. Proceeding from below upward, we find the following structures lying in superimposed planes: the skin, the superficial fascia, the deep layer of the superficial fascia, the transversus perinæi and the sphincter vaginæ muscles, the anterior layer of the triangular ligament, the posterior layer of the triangular ligament, the levator ani muscle ([Fig. 19]).
Fig. 18, A.—Superficial structures of the female perineum (Weisse).
Fig. 19.—Dissection of female perineum: on the left side the perineal muscles are exposed by the reflection of the perineal fascia; on the right side the muscles and the superficial layer of the triangular ligament have been removed, thereby exposing the deep layer of the ligament. S. V., Sphincter vaginæ muscle.
The vagina passes through these structures. They surround and support the ostium vaginæ as the fascia and muscles surround and support the opening of the rectum or the anus. The muscles and fasciæ are attached in the median line between the anus and the vagina, and therefore this part of the body, which is called the perineum, is supported or maintained in its proper position by these various structures. The transversus perinæi arises from the ramus of the ischium and is inserted in the perineum. The bulbo-cavernosus, or sphincter vaginæ, arises in the perineum and is inserted in and about the clitoris. The inner fibers of the levator ani arise from the symphysis pubis and are inserted in the perineum and the lower part of the vagina ([Fig. 20]). When these muscles contract, their action, therefore, is to draw the perineum upward and forward. At the same time the anus is drawn upward and forward, and so also is the posterior margin of the ostium vaginæ and the lower portion of the posterior vaginal wall.
