New anatomical insight into the muscular structure of the anal canal: revealing Treitz muscle as a directional shift of the internal anal sphincter

In summary, Treitz muscle, a smooth muscle extending from the internal anal sphincter, is considered part of the muscularis propria. Its directional shift was localized to the anterolateral wall, indicating that Treitz muscle is not uniformly distributed around the anal canal. This site-specific localization may influence the risk of hemorrhoids or cancer invasion depending on its anatomical position.