The anal triangle consists of a central anal canal and the lateral ischiorectal fossae. The sphincter ani externus muscle has three parts: subcutaneous, superficial, and deep. Muscle fibers are attached to the perineal body anteriorly and to the anococcygeal ligament posteriorly. The muscle is supplied by the inferior rectal nerve and vessels.
The ischiorectal fossae occupy the lateral portion of the anal triangle. The medial boundaries are the sphincter ani externus muscle and anal canal, the levator ani and coccygeus muscles, and their fasciae. The obturator internus muscle identifies the lateral wall. The posterior wall is the sacrotuberous ligament, covered by the gluteus maximus muscle. The anterior wall is the superficial and deep spaces of the urogenital triangle. The superior roof of the fossa is formed by the obturator internus and levator ani muscles. The skin and superficial fascia form the base of the fossa.
The contents of the ischiorectal fossae include the inferior rectal nerve, which is a branch of the pudendal nerve, supplying the levator ani and sphincter ani externus muscles; the inferior rectal artery, which is a branch of the internal pudendal artery; and the inferior rectal vein, which drains to the internal pudendal vein. All these structures then communicate with the pudendal nerve and internal pudendal artery and vein, which are located in the pudendal canal The canal is formed by the obturator internus fascia and is located in the lateral wall of the ischiorectal fossa.