NCIt definition : An anatomical line of demarcation that separates the upper and lower part of the anal
canal, both in structure and neurovascular supply, reflecting the different embryologic
origin; superior to the line the epithelium is a mucous membrane like the rest of
the gastrointestinal tract and inferiorly the epithelium is considered cutaneous,
and is composed of stratified squamous keratinized with hair and sebaceous glands.;