ischioanal fossa ischioanal fossa the ischioanal fossa (formerly called ischiorectal fossa) is the fat-filled wedge-shaped space located lateral to the anal canal and inferior to the pelvic diaphragm. it is somewhat prismatic in shape, with its base directed to the surface of the perineum and its apex at the line of meeting of the obturator and anal fasciae. ischioanal fossathe perineum. the integument and superficial layer of superficial fascia reflected. (ischiorectal fossa labeled at bottom left.)the posterior aspect of the rectum exposed by removing the lower part of the sacrum and the coccyx (ischiorectal fossa labeled at bottom right)detailsidentifierslatinfossa ischioanalista98a09.5.04.001ta22446fma22059anatomical terminology boundaries it has the following boundaries: anterior* fascia of colles covering the transversus perinei superficialis* inferior fascia of the urogenital diaphragm(perineal membrane) lateral* tuberosity of the ischium* obturator internus muscle * obturator fasciasuperior:* levator ani inferior:* skin medial:* levator ani* sphincter ani externus muscle* anal fascia posterior* gluteus maximus* sacrotuberous ligament contents the contents include: inside alcock's canal, on the lateral wall internal pudendal artery internal pudendal vein pudendal nerve outside alcock's canal, crossing the space transversely inferior rectal artery inferior rectal veins inferior anal nerves fatty tissue across which numerous fibrous bands extend from side to side allows distension of the anal canal during defecation