This is the triangle lying between the ischial tuberosities on each side and the coccyx. It comprises, in essentials, the anus with its superficial sphincters, levator ani and, at each side, the ischiorectal fossa.
The ischiorectal fossa (Fig. 100) (which would be more accurately called the ischio-anal fossa) is of considerable surgical importance because of its great tendency to become infected. Its boundaries are: • laterally — the fascia over obturator internus (i.e. the side wall of the pelvis); contained in this wall within a fascial tunnel termed the pudendal or Alcock's canal are the pudendal vessels and nerve which give off respectively the inferior rectal vessels and nerve, which supply the external
sphincter and perianal skin, then pass forward to supply the perineal tissues;
• medially—the fascia over levator ani and the external anal sphincter;
• posteriorly—the sacrotuberous ligament covered posteriorly by gluteus maximus;
• anteriorly—the urogenital perineum;
• floor—skin and subcutaneous fat.
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