As the ischioanal fat is removed, identify the boundaries of the ischioanal fossa (Figure 41.3). The medial wall is formed by the pelvic diaphragm [tip of probe]. The lateral wall is formed by the obturator internus muscle, covered by the obturator fascia . The posterolateral border of the fossa is partially formed by the gluteus maximus muscle and the underlying sacrotuberous ligament. Cut the gluteus maximus muscle and reflect it posteriorly to reveal the sacrotuberous ligament.
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