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Week 3 - Tail end of human embryo from fifteen to eighteen days old

From model by Franz Keibel (1861-1929)


The Rectum and Anal Canal - The hind-gut is at first prolonged backward into the body-stalk as the tube of the allantois; but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried forward to the ventral aspect of the body, and consequently a bend is formed at the junction of the hind-gut and allantois. This bend becomes dilated into a pouch, which constitutes the entodermal cloaca; into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward. At a later stage the Wolffian and Müllerian ducts open into its ventral portion. The cloaca is, for a time, shut off from the anterior by a membrane, the cloacal membrane, formed by the apposition of the ectoderm and entoderm, and reaching, at first, as far forward as the future umbilicus. Behind the umbilicus, however, the mesoderm subsequently extends to form the lower part of the abdominal wall and symphysis pubis. By the growth of the surrounding tissues the cloacal membrane comes to lie at the bottom of a depression, which is lined by ectoderm and named the ectodermal cloaca (Fig. 991).


Links: Image 987a | Image 987b | Image - Early Week 4 | Image - Late Week 4 | Gastrointestinal Tract Development | Endoderm




Gray's Images: Development | Lymphatic | Neural | Vision | Hearing | Somatosensory | Integumentary | Respiratory | Gastrointestinal | Urogenital | Endocrine | Surface Anatomy | iBook | Historic Disclaimer
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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)
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Reference

Gray H. Anatomy of the human body. (1918) Philadelphia: Lea & Febiger.


Cite this page: Hill, M.A. (2019, July 17) Embryology Gray0991.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Gray0991.jpg

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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