File:Pohlman1911 plate2.jpg

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Plate 2

Model C. No. 9 (Mall 80; 5.0 mm; + ; 10; Good). Carnegie stage 14. x 100. About the same as the foregoing stage. Tail gut undergoing degenerative changes. This model shows marked degeneration of the tail gut. The allantois is narrow lumened, while the widely lumened ventral cloacal segment lies ventral to the hind gut and dorsal segment, and is separated from them by peritoneum. The Wolffian ducts open in the same situation as in the foregoing model, and present dorsal diverticulae, the renal buds. The ventral portion of the cloaca, especially the area above the cloacal membrane, is markedly widened and flattened. The lateral furrow of Model A was not present. This model conforms to the Keibel model of a 6.5 mm. embryo (a considerably older stage if we go by the greatest length rule). The cloaca has lost its more or less even width and attains its greatest lateral diameter at the level of the Wolffian orifices. There is no evidence of displacement of the Wolffian ducts from their primitive position in relation with the upper limit of the cloacal membrane.


Model D {No. 12; Mall no. 2; 7.0 mm.) Carnegie stage 15 This model fills in a gap in the Keibel series which may be considered quite an important one. The hind gut and all that pertains to the dorsal segment of the cloaca has retained an even caliber, while the ventral segment has widened progressively. The division of the cloaca may be traced to the level of the Wolffian orifices. The Wolffian ducts are much better developed and the renal anlage has resolved itself into distinct ureter and kidney segments. The segment of Wolffian duct between the orifice of the ureter and the cloaca is relatively shorter. The renal anlagen have assumed the position of dorsal convergence (mentioned by Keibel) but this is only a relative matter (see later). The tail gut has undergone further degeneration and has lost its lumen in part.


Key to Lettering

A., Allantois

K., Kidney

A.M., Position of anal membrane

P.T., Precloacal mesodermic tissue

C., Cloaca

R.B., Renal bud

CM., Cloacal membrane

T.G., Tail cut

C.S., Cloacal segment of Wolffian duct

U., Ureter

G.E., Genital eminence

U.G., Urogenital sinus

H.G., Hind gut

U.M., Position of urogenital membrane

* Probable position of point where allantois joins cloaca.

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, February 23) Embryology Pohlman1911 plate2.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Pohlman1911_plate2.jpg

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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