#anus__arse__arsehole__asshole  excretory opening at the end of the alimentary canal
  supertype:  #orifice__opening__porta  an aperture or hole opening into a bodily cavity; "the orifice into the aorta from the lower left chamber of the heart"
  subtype:  #imperforate_anus  a congenital defect of the anus; there is partial or complete obstruction of the anal opening
  part of:  #rectum
  part:  #anal_sphincter__sphincter_ani__sphincterani__musculus_sphincter_ani  the sphincter muscle of the anus
     part:  #musculus_sphincter_ani_externus  an external ring of striated muscle surrounding the anus
     part:  #musculus_sphincter_ani_internus  an internal ring of smooth muscle formed by circular fibers of the rectum

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