Figure 2From: Magnetic resonance imaging and endorectal ultrasound for diagnosis of rectal lesions Endosonographic morphology of the anal canal: a high level (A) at the level of the sling of the puborectalis muscles (PR) and superficial transverse perineal muscles (STP), mid level (B) with a well-formed internal (IAS) and external anal sphincter (EAS), and superficial/low level (C) with the external anal sphincter. Back to article page