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→Histology
***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.
*Sebaceous and apocrine sweat glands both occur in this region an with the anal sphincters.
*Sebaceous and apocrine sweat glands both occur in this region in association with the anal sphincters.
*The '''anal canal''' joins the bowel to the exterior.
**This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).
**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.
==Species Differences==
==Species Differences==