The mons veneris in front, the buttocks behind, and the thighs laterally bound the perineum. More deeply, it is limited by the margins of the pelvic outlet, namely, the pubic symphysis and arcuate ligament, ischiopubic rami, ischial tuberosities, sacrotuberous ligaments, sacrum, and coccyx. A transverse line joining the ischial tuberosities divides the perineum into an anterior urogenital and a posterior anal triangle.
The perineal ﬂoor is composed of skin and two layers of superﬁcial fasciae a superﬁcial fatty stratum and a deeper membranous one. The former is continuous anteriorly with the superﬁcial fatty layer of the abdomen (Camper fascia) and posteriorly with the ischiorectal fat. The deeper, membranous layer of the superﬁcial perineal fascia (Colles fascia) is limited to the anterior half of the perineum. Laterally, it is attached to the ischiopubic rami; posteriorly, it blends with the base of the urogenital diaphragm; and anteriorly, it is continuous with the deep layer of the superﬁcial abdominal fascia (Scarpa fascia).
The urogenital diaphragm is a strong, musculomembranous partition stretched across the anterior half of the pelvic outlet between the ischiopubic rami. It is composed of superior and inferior fascial layers between which are located the deep perineal muscles, the sphincter of the membranous urethra, and the pudendal vessels and nerves. It is pierced by the urethra and vagina.
The anal triangle is delineated by the superﬁcial perineal muscles anteriorly, the sacrotuberous ligaments and margins of the gluteus maximus laterally, and the coccyx posteriorly. It contains the anal canal and its sphincters, the anococcygeal body, and the ischiorectal fossae.
The ischiorectal fossae are prismatic in shape. The lateral wall of each is formed by the obturator internus fascia, and its medial wall by the fascia overlying the levatorani, the coccygeus, and the external anal sphincter muscles. The tendinous arch marks its apex. Anteriorly, the fossa extends between the urogenital and pelvic diaphragms. Posteriorly, the sacrotuberous ligament and gluteus maximus muscle limits it. The contents of the ischiorectal fossa include an abundance of fat, the inferior hemorrhoidal vessels and nerves, and the internal pudendal vessels and nerves within Alcock canal.
The muscles of the perineum include the bulbocavernosus, the ischiocavernosus, the superﬁcial and deep transverse perineal muscles, the sphincter of the membranous urethra, and the external anal sphincter. These muscles, in general, correspond to their homologues in the male. The ischiocavernosus muscles are smaller than in the male. They overlie and insert into the crura of the clitoris instead of into the crura of the penis, as in the male. The bulbocavernosus muscles surround the oriﬁce of the vagina and cover the vestibular bulbs. They are attached posteriorly to the central tendinous point of the perineum and to the inferior fascia of the urogenital diaphragm and insert anteriorly into the corpora cavernosa clitoris. They are sometimes termed the sphincter vaginae. Spasms in this muscle group are often found in patients with vaginismus. The pair of deep transverse perineal muscles (within the urogenital diaphragm) is interrupted near the midline by the vagina, into which they insert.
The central point of the perineum lies at the base of the urogenital diaphragm between the vaginal and anal oriﬁces. It is a common ﬁbrous point of attachment for the bulbocavernosus, the superﬁcial and deep transverse perineal, the levatorani, and the external anal sphincter muscles. This area is often referred to as the perineal body.
The anococcygeal body is of ﬁbromuscular consistency and extends from the anus to the coccyx. It receives ﬁbers from the external anal sphincter and the levatorani muscles and serves as a support for the anal canal.