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→Histology
[[Image:Anal Glands.jpg|thumb|right|150px|Anal Glands- Copywright RVC 2008]]
[[Image:Anal Glands.jpg|thumb|right|150px|Anal Glands- Copywright RVC 2008]]
*At the anus, the columnar intestinal epithelium is replaced by the stratified squamous keratinised epithelium of the skin.
*At the anus, the columnar intestinal epithelium is replaced by the stratified squamous keratinised epithelium of the skin.
*The '''anal canal''' joins the bowel to the exterior and is the last 2-3cm of the alimentary tract.
**This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).
*Sebaceous and apocrine sweat glands both occur in this region in association with the anal sphincters.
**Before joining the anal canal, the rectum becomes dilated to form the ''rectal ampulla''.
*At the '''rectoanal''' junction, the lumen is constricted by longitudinal folds in the mucosa.
**These are normally pressed together to occlude the lumen.
*As the muscosa changes from columnar to cutaneous, three zones are created:
*As the muscosa changes from columnar to cutaneous, three zones are created:
**'''Columnar'''
**'''Columnar'''
***Surrounds the anus.
***Surrounds the anus.
***Excretory ducts of the '''anal sacs''' open into this region.
***Excretory ducts of the '''anal sacs''' open into this region.
==Species Differences==
==Species Differences==