From Embryology

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Fig. 76. Dorsal view of human embryo, two millimeters in length, with yolk sac

von Spee, Kollmann.

In a somewhat older human embryo described by von Spee a dorsal view of the embryonic disk shows close resemblances to conditions in the lower mammals (Fig. 76). The position of the primitive streak is indicated by the conspicuous primitive groove. Anterior to this the neural groove extends almost the full length of the disk which has become considerably elongated. The yolk sac is now suspended from the ventral side of the disk. A longitudinal section in the medial sagittal plane shows the embryonic disk separating the yolk cavity from the amniotic cavity (Fig. 77). The mesoderm is an extensive layer investing both amnion and yolk sac and forming a strong band which attaches the embryonic body to the outer wall of the vesicle (now the chorion). A cross section through the primitive streak shows a striking resemblance to a corresponding section of the embryonic disk of a rabbit. (Compare Figs. 78 and 79) The three germ layers are fused in the streak, and the mesoderm extends laterally on both sides between the other two layers.

"Links: Fig. 76 in text

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Bailey FR. and Miller AM. Text-Book of Embryology (1921) New York: William Wood and Co.

Cite this page: Hill, M.A. (2024, April 13) Embryology Bailey076.jpg. Retrieved from

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