Changes

**This is a short passage derived from the proctodeum (formed by invagination of the surface ectoderm).

**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''.

**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.

*At the ''rectoanal'' junction, the lumen is constricted by longitudinal folds in the mucosa.

**These are normally pressed together to occlude the lumen.

**These are normally pressed together to occlude the lumen.