File:Pohlman1911 plate3.jpg

Plate 3

Model E. {No. 19; Mall no. 221; 12.0 mm.) This stage shows the cloaca about half divided along the furrow line indicated in Model A. The cloacal membrane has thickened but mostly through addition of ectodermal cells, and has been displaced through development of the ' precloacal mesoderm' from its primitive position parallel to the dorsal line of the cloaca to one more nearly at right angles to it. In so far as it was possible to ascertain, this downward displacement of the cloacal membrane in no way affects its caudal limit. The dorsal segment has retained the original proportions while the ventral segment has widened - most marked again at the level of the Wolffian orifices. The further development of the kidney and ureter will be noted and the gradual approach of the ureteral orifice to the cloaca proper is evident. The ureter shows signs of shifting from its primitive dorsal position on the Wolffian duct to a more lateral one. The peritoneum has descended to the level of the ducts while the cloacal division is relatively far advanced. The model agrees with Keibel's model of an 11.5 mm. embryo.

No. 19 (Mall 221; 12.0 mm; = ; 20; Good). Model E x 100. All traces of tail gut lost. Cloacal membrane somewhat depressed from surface. Cloacal segment of Wolffian duct shortened and opening of ureter and duct common into ventral cloacal segment. Beginning formation of genital eminence and lengthening of the ventral cloacal wall. Cloacal membrane intact. Carnegie stage 16

Model F. {No. 24; Mall no. 43; 16.0 mm. X 50.) Unfortunately this embryo was cut too thick for minute reconstruction. The stage however fills in another gap in the Keibel series. Here the cloaca and the cloacal membrane are completely divided - the ventral segment limited by the urogenital plate and the dorsal segment by the anal plate. The ureter is displaced from its dorso-lateral position on the Wolffian duct to a supero-lateral one and opens distinctly into the ventral cloacal segment. The marked increase in precloacal tissue has resulted not only in the large genital eminence, but the urogenital plate has been dislocated deeper into the base of the phallus and a marked heaping up of ectodermal cells has occurred in the furrow on the caudal surface of the eminence. The two resultant segments of the cloacal membrane, the urogenital and anal plates are apparently no longer than they were in much younger stages; a point that will be brought out in greater detail later.

No. 24 (Mall 43; 16.0mm.; = ; 50; Good). Model F . x 50. Anal and urogenital membranes separated. Genital eminence more marked. Ectodermic inclusion in furrow on caudal surface. Ureteral orifice on same level but some distance lateral to Wolffian orifice. Carnegie stage 19

All drawings represent 100 diameters enlargement except of Model F which is 50 diameters.

Links: plate 1 | 1 A | 1 B | plate 2 | plate 2C | plate 2D | plate 3 | plate 3E | plate 3F | Pohlman 1911

Reference

Pohlman AG. The development of the cloaca in human embryos. (1911) Amer. J Anat. 12: 1-26.

Cite this page: Hill, M.A. (2024, April 27) Embryology Pohlman1911 plate3.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Pohlman1911_plate3.jpg

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