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Figure 8b. (a) Transverse T2-weighted fast spin-echo (2,500/100) MR image obtained through the lower edge of the anal sphincter with an endoanal coil and (b) corresponding drawing in a 25-year-old asymptomatic female volunteer show the external sphincter (ES), anococcygeal ligament (AC), bulbocavernous muscle (BC), ischiocavernous muscle (IC), superficial transverse perineal muscle (STP), and vaginal introitus (VI).