part of part of surrounds surrounds anus external anal sphincter SCTID:244969008 The Sphincter ani externus (external anal sphincter) is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. [WP,unvetted]. FMA:21930 Wikipedia:Sphincter_ani_externus_muscle musculus sphincter ani externus NCIT:C32548 external sphincter ani UBERON:0001367 EMAPA:18265 MA:0001531 Some literature reports don't consider the external anal sphincter to be a true sphincter muscle. skeletal muscle tissue of trunk muscle of anal triangle anal region skeletal muscle anal sphincter anal part of perineum striated muscle sphincter