It invaginates from cranial to caudal, formed from the endodermal cloaca, and fuses with the cloacal membrane.

The urorectal septum is an embryonic structure formed from an invagination of the cloaca.

[1] The urorectal septum develops from cranial to caudal, and is flat in the coronal plane.

[3] Mainly because of these associations, up to 20% of children born with urorectal septum malformation may not survive long-term.

[3] This article incorporates text in the public domain from page 1109 of the 20th edition of Gray's Anatomy (1918)