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
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Gray H. Anatomy of the human body. (1918) Philadelphia: Lea & Febiger.
Cite this page: Hill, M.A. (2019, January 16) Embryology Gray0991.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Gray0991.jpg
- © Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
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