Fig. 5. Horizontal sections of two embryos at 7 weeks before differentiation of urogenital sinus into the bladder and urethra. (A, B) A specimen of crownrump length (CRL) 26 mm. (C, D) Another specimen of CRL 26 mm. Orange-G staining (A, B) and silver staining (C, D). The upper side of each panel corresponds to the posterior side of the pelvis. (A, B) The urogenital sinus (URS) is dilated and protrudes anteriorly due to unknown reason. Panels (A) and (C) display the plane 0.1 mm superior to panels (B) and (D), respectively. In both specimens, the Wolffian duct (WD) opening is located 0.1 mm inferior and 0.1 mm medial side of the ureteral opening (UR). All panels were prepared at the same magnification. Scale bar in panel A=1 mm. IL, ileum of the intestine; K, definite kidney (metanephros); MD, Műllerian duct or paramesonephric duct; OE, obturator externus muscle; OI, obturator internus muscle; P, pubis; PC, peritoneal cavity; PR, prostate; PX, pelvic autonomic nerve plexus; R, rectum; UA, umbilical artery.