Development of the human Mullerian duct in the sexually undifferentiated stage

An embryological explanation for the development of the Mullerian duct still poses a major challenge. The development of this duct was investigated systematically in human embryos. Seven embryos (Carnegie stages 18-23) were serially sectioned in the frontal, sagittal, and transversal planes at a thickness of 10 mum and stained with hematoxylin and eosin (H&E) for histological analysis. In all observed embryos, the caudal end of the Mullerian duct was found to be intimately connected to the Wolffian duct. The opening of the Mullerian duct to the coelomic cavity was formed as the result of an invagination of the coelomic epithelium at Carnegie stage 18. The duct grew independently from the invagination during stages 19-23. The fused duct (uterovaginal canal) bifurcated at the caudal portion at Carnegie stages 22 and 23. This is the first description of the caudal portion of the fused Mullerian ducts separating again and returning to each of the Wolffian ducts in human embryos. Anat Rec Part A 272A:514-519, 2003. (C) 2003 Wiley-Liss, Inc.