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Fig. 81. Diagrams representing hypothetical stages in the development of the human embryo

(to follow Fig. 80).

A, Entoderm surrounds the yolk cavity; part of the cells of the inner cell mass have become vacuolated, thus forming the amniotic cavity, while the remainder constitute the embryonic ectoderm; compare with Fig. 59.

B, Mesoderm (represented by dotted portion) has appeared between the entoderm and trophoderm, between the entoderm and ectoderm of the embryonic disk, and in the roof of the amnion.

C, The mesoderm around the yolk cavity has split into a parietal and a visceral layer, the cleft between being the rudiment of the extraembryonic body cavity (exoccelom).

The series of diagrams in Figs. 80, 81 and 82 has been constructed to give the student a general idea of the changes that occur in the early stages of human development. It must be recognized, however, that the diagrams represent purely hypothetical stages up to the conditions shown in diagram B in Fig. 81 which corresponds roughly to the Bryce-Teacher embryo (Fig. 73) ; even in this diagram the extent of the mesoderm is much less than in the known human embryo. In Fig. 82 diagram A approximates the Peters embryo (Fig. 74), diagram D the von Spee embryo (Fig. 77). The history of the accessory structures which are shown in part will be considered in the chapter on "Foetal Membranes".

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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)


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 Bailey081.jpg. Retrieved from

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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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