Uberon definition : The ridge of mesoderm covered with endoderm that in the early developing embryo partitions
the endodermal cloaca into the primary urogenital sinus (ventrally) and the anorectal
canal of the hindgut (dorsally); the urorectal septum eventually fuses with the cloacal
membrane, dividing it into a dorsal anal membrane and a larger ventral urogenital
membrane - this area of fusion is represented in the adult by the perineal body[MP].;
Uberon Homology note : In mammals the lowly monotremes still have a cloaca. Higher types have done away with
this structure and have a separate anal outlet for the rectum. The monotreme cloaca
shows the initiation of this subdivision. The cloaca has such includes only the distal
part, roughly comparable to the proctodeum. The more proximal part is divided into
(1) a large dorsal passage into which the intestine opens, the coprodeum, and (2)
a ventral portion, the urodeum with which the bladder connects. (...) the development
of the placental mammals recapitulates in many respects the phylogenetic story. In
the sexually indifferent stage of placental mammal there is a cloaca. While the indifferent
stage still persists, a septum develops, and extends out to the closing membrane.
This divides the cloaca into two chambers: a coprodeum continuous with the gut above,
and a urodeum or urogenital sinus below.[well established][VHOG];
The ridge of mesoderm covered with endoderm that in the early developing embryo partitions
the endodermal cloaca into the primary urogenital sinus (ventrally) and the anorectal
canal of the hindgut (dorsally); the urorectal septum eventually fuses with the cloacal
membrane, dividing it into a dorsal anal membrane and a larger ventral urogenital
membrane - this area of fusion is represented in the adult by the perineal body[MP].