From Embryology

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Fig. 9, A to N forms a series of purely diagrammatic representations introduced to facilitate the comprehension of the manner in which the body of the embryo is formed, and of the various relations of the yolk-sac, amnion and allantois.

In L the splanchnopleure has completely invested the yolksac, but at the lower pole of the yolk is still continuous with that peripheral remnant of the somatopleure now called the serous membrane. In other words, the cleavage of the mesoblast has been carried all round the yolk (ys) except just at the lower pole.

In M the cleavage has been carried through the pole itself ; the peripheral portion of the splanchnopleure forms a complete investment of the yolk, quite unconnected with the peripheral portion of the somatopleure, which now exists as a continuous membrane lining the interior of the shell. The yolk-sac (ys) is therefore quite loose in the pleuroperitoneal cavity, being connected only with the alimentary canal (a') by a solid pedicle.

Lastly, in N the yolk-sac (ys} is shewn being withdrawn into the cavity of the body of the embryo. The allantois is as before, for the sake of simplicity, omitted ; its pedicle would of course lie by the side of ys in the somatic stalk marked by the usual dotted shading.

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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


Foster, M., Balfour, F. M., Sedgwick, A., & Heape, W. (1883). The Elements of Embryology. (2nd ed.). London: Macmillan and Co.

The Elements of Embryology (1883)

Volume 1 The History of the Chick: Egg structure and incubation beginning | Summary whole incubation | First day | Second day - first half | Second day - second half | Third day | Fourth day | Fifth day | Sixth day to incubation end
Volume 2 The History of the Mammalian Embryo: General Development | Embryonic Membranes and Yolk-Sac | Organs from Epiblast | Organs from Mesoblast | Alimentary Canal | Appendix

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