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Illustration based on a graphic reconstruction and a model of specimen no. 7802. The primitive node of Hensen is in a very early stage of development and has not yet produced a conspicuous elevation of the germ disk. The allantoic duct consists of a proximal part attached to the umbilical vesicle and a detached bulbous segment. A broad amniotic duct projects from the dorsal apex of the amnion and ends blindly in the chorionic mesoderm.

Fig. 31. Heuser et al., 1945.

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Keywords: allantoic duct, amnion, amniotic duct, chorionic mesoderm, cloacal membrane, gastrulation (primitive) node, germ disk, primitive node, primitive node of Hensen, primitive streak, umbilical vesicle

Source: The Virtual Human Embryo.