Figure 5b. (a) Coronal midanal T2-weighted fast spin-echo (2,500/100) MR image obtained with an endoanal coil and (b) corresponding drawing in a 21-year-old asymptomatic male volunteer demonstrate the internal sphincter (IS), intersphincteric space (ISS), longitudinal muscle (LM), external sphincter (ES), puborectal muscle (PR), and levator ani muscle (LA).