Rectal incontinence is due to involvement of :a) External anal sphincterb) Internal anal sphincterc) Ischiococcygeusd) Pubococcygeus
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Rectal continence depends solely on the anorectal ring and any damage to this ring results in rectal incontinence.
The anorectal ring is a muscular ring present at the anorectal junction, and formed by the fusion of -

Puborectalis (a part of pubococcygeus which in turn is a part of levator ani)
Deep external anal sphincter
Internal anal sphincter

The puborectalis muscle appears to be the most important muscle for maintaining fecal continence.