Pelvic Viscera

Abstract

The allantois is an evagination from the primitive hindgut (Fig. 488 A). Shortly after this forms, the gut caudad to the point of origin of the allantois enlarges to form the cloaca. The cloaca is divided into a ventral and a dorsal part by an ingrowing urorectal fold; the ventral part becomes the urogenital sinus, and the dorsal part becomes the rectum (Fig. 488 B). The urorectal fold cuts into the cephalic part of the cloaca, where the allantois and the hindgut meet, and then grows caudad to the cloacal membrane.