n. the membranous sac that develops as an outgrowth of the embryonic hindgut. Its outer (mesodermal) layer carries blood vessels to the *placenta and so forms part of the *umbilical cord. Its cavity is small and becomes reduced further in size during fetal development (see urachus). —allantoic adj.... allantois
n. the most posterior part of the embryonic *hindgut. It becomes divided into the rectum and the urinogenital sinus, which receives the bladder together with the urinary and genital ducts.... cloaca
n. the site of the embryonic anus, marked by a depression lined with ectoderm. The membrane separating it from the hindgut breaks down in the third month of gestation. Compare stomodeum.... proctodeum
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