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FIG. 29. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH THE Axis OF AN EMBRYO.

The section is supposed to be made at a time when the headfold has commenced but the tail-fold has not yet appeared.

N.C. neural canal, closed in front but as yet open behind. Ch. notochord.

The section being taken in the middle line, the protovertebrae are of course not shewn.

In front of the notochord is seen a mass of uncleft mesoblast, which will eventually form part of the skull.

D. the commencing foregut or front part of the alimentary canal.

F. So. Somatopleure, raised up in its peripheral portion into the amniotic fold Am. Sp. Splanchnopleure. At Sp. it forms the under wall of the foregut ; at F. Sp. it is turning round and about to run forward.

Just at its turning point the cavity of the heart Ht. is being developed in its mesoblast. pp. pleuroperitoneal cavity. A epiblast, B mesoblast, C hypoblast, indicated in the rest of the figure by differences in the shading.

At the part where these three lines of reference end the mesoblast is as yet uncleft.

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Reference

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