The essentially vertical lateral wall of an ischiorectal fossa is formed by the ischium with its attached obturator internus and associated fascia (Figure 4).
Posteriorly the ischiorectal fossae extends below the lower edge of gluteus maximus as far as the sacrotuberous ligament (Figure 4).
The ischiorectal fossae are filled with adipose tissue that is infiltrated with numerous tough, fibrous bands and septa, some of which are derived from the longitudinal muscle of the anal canal (Figure 4).
Review of the anatomy of the perineum reveals that external palpation of the levator ani muscles must occur through the fat filled ischiorectal fossa (Figures 4 and 5).
The ischiorectal fat pad also allows for dilation of the vagina during parturition when the foetal head virtually eliminates the space.
The external genitalia and the urogenital diaphragm are found within the urogenital triangle, while the anal triangle is composed of the centrally placed anal canal encircled by the external anal sphincter and flanked laterally and posteriorly by the ischiorectal fossae (Figure 3).
The ischiorectal fossae are fascia-lined wedge shaped spaces found on either side of the anal canal and rectum.
Before considering the detailed anatomy of the ischiorectal fossae one needs an appreciation of the regional anatomy, namely the perineum.