Figure 4a. (a) Coronal T2-weighted fast spin-echo (2,500/100) MR image obtained through the anterior anal sphincter complex with an endoanal coil and (b) corresponding drawing in a 30-year-old asymptomatic female volunteer demonstrate the internal sphincter (IS), external sphincter (ES), puborectal muscle (PR), levator ani muscle (LA), arcus tendineus levator ani (ATLA), internal obturator muscle (IOM), and urogenital diaphragm (UG).