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FIG. 28. AN EMBRYO CHICK OF ABOUT THIRTY-SIX HOURS, VIEWED FROM BELOW AS A TRANSPARENT OBJECT.

FB. the fore-brain or first cerebral vesicle, projecting from the sides of which are seen the optic vesicles, op. A definite head is now constituted, the backward limit of the somatopleure fold being indicated by the faint line S.O. Around the head are seen the two limbs of the amniotic head-fold : one, the true amnion a, closely enveloping the head, the other, the false amnion a', at some distance from it. The head is seen to project beyond the anterior limit of the pellucid area.

The splanchnopleure folds extend as far back as sp. Along its diverging limbs are seen the conspicuous venous roots of the vitelline veins, uniting to form the heart h, already established by the coalescence of two lateral halves which, continuing forward as the bulbus arteriosus b. a., is lost in the substance of the head just in front of the somatopleure fold.

HE. hind-brain ; ME. mid-brain ; p.v. and v.pl. mesoblastic somites ; ch. front end of notochord ; me. posterior part of notochord ; e. parietal mesoblast ; pi. outline of area pellucida ; pv. primitive streak.

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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