Pelvic Diaphragm and External Anal Sphincter

Variations of the pelvic diaphragm and external anal sphincter are very rare, but minor variations have been reported through cadaver studies and clinical examination using magnetic resonance imaging (MRI). In this chapter, the author prefer to use pubovisceralis. The puborectalis can be considered as part of the anal sphincter complex. Among the three portions of the levator ani muscle, the pubococygeus (pubovisceralis) and puborectalis exhibit variations while the iliococcygeus does not. The coccygeus is located between the levator ani anteriorly and the sacrospinous ligament posteriorly. The external anal sphincter (EAS) is a circular muscle with fibers from the anococcygeal ligament posteriorly that extend forward to encircle the anus and insert onto the perineal body anteriorly. The blood supply to the EAS is mainly from the inferior rectal artery. In general, anatomical vari- ations of the EAS in terms of origin, insertion, blood, and nerve supply are uncommon.