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Fig. 74. Section through very young human chorionic vesicle embedded in the uterine mucosa

Peters.

The vesicle measured 2.4 x 1.8 mm, the embryo 19 mm. Peters reckoned the age as 3 or 4 days, but later studies of other embryos go to show that the age is much greater. Bryce and Teacher estimate it at 14 to 15 days.

In a slightly older embryo described by Peters (Fig. 74) a space has appeared within the mesoderm, so that one portion remains as a lining for the trophodermal wall and the remainder closely invests the yolk sac and amnion and also forms a layer between ectoderm and entoderm in the embryonic disk (Fig. 75). The disk is therefore composed of all three germ layers, but there is still no indication of a primitive streak. It would seem that in the highest primate the mesoderm develops independently of the primitive streak; but whether it arises from ectoderm or entoderm it is not possible in the present state of our knowledge to determine.


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Pages where the terms "Historic Textbook" and "Historic Embryology" 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 and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Reference

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



Cite this page: Hill, M.A. (2019, June 16) Embryology Bailey074.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey074.jpg

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