→Schematic illustration of the origin and localization of Treitz muscle in the anal canal. (A) Schematic view from the medial aspect showing the course of Treitz muscle on the lateral wall of the anal canal. Treitz muscle originates at the level of the anorectal angle on the anterolateral wall of the anal canal, arising from a directional change in the muscle bundles of the internal anal sphincter (IAS). Some bundles descend along the anterior wall, while others course from the lateral wall toward the posterolateral wall, forming multiple muscle bundles. (B) The origin of Treitz muscle is the directional shift of the IAS. Specifically, some superficial muscle bundles, which usually run in a circular orientation, undergo a change in direction and begin to run longitudinally, forming Treitz muscle. This origin is localized to the anterolateral region of the anal canal, from which muscle bundles descend anteriorly and posterolaterally due to this shift in orientation. As a result, Treitz muscle demonstrates region-specific distribution, being localized to the anterior and bilateral posterolateral regions of the anal canal. CM, circular muscle.
