Boundaries of the perineum (Fig. 1) are anteriorly, the pubic symphysis; posteriorly, the coccyx; anterolaterally, the pubic arch and ischiotuberosity; and posterolateral, the sacrotuberous ligament. The floor of the perineum is the skin and the roof is the pelvic diaphragm (levator ani and coccygeus muscles). The perineum can be divided into a posterior anal triangle and an anterior urogenital triangle.
Figure 1. Urogenital and anal triangles. The perineum is a diamond-shaped region. It is bordered by the two ischiopubic rami and the two sacrotuberous ligaments. (Some authors define the posterior margins of this region to be imaginary lines on each side extending from the ischial tuberosity to the coccyx.) A horizontal line connecting the two ischial tuberosities divides the perineum into the anterior urogenital triangle and the posterior anal triangle. At the midpoint of this line is found the perineal body, just anterior to the anal canal.