Which muscle is NOT considered part of the anal sphincter complex?

• A. Pubococcygeus
• B. Puborectalis
• C. Internal anal sphincter
• D. External anal sphincter

Answer: (A)

Continence relies on a ring-like mechanism around the anal canal plus supportive pelvic floor muscles. The anal sphincter complex consists of the internal anal sphincter, a smooth muscle that provides involuntary baseline tone, and the external anal sphincter, a skeletal muscle that offers voluntary control. The puborectalis part of the levator ani forms a sling behind the anorectal junction, helping maintain the anorectal angle and contributing to continence. The pubococcygeus, another pelvic floor muscle in the levator ani group, supports pelvic organs and elevates the pelvic floor but does not encircle the anal canal as part of the sphincter mechanism. Because of that distinction, pubococcygeus is not considered part of the anal sphincter complex.