abnormal digestive system morphology abnormal anal canal morphology MP:0009053 MPheno.ontology abnormal canalis analis any structural anomaly in the terminal portion of the alimentary canal, which begins at the anorectal junction, where the rectal ampulla abruptly narrows as the alimentary canal pierces the pelvic diaphragm (levator ani), and ends at the anal verge, when the anoderm that lines the lower anal canal changes to hairy perianal skin; surrounded by the internal and external anal sphincters