Elements of biology, with special Elements of biology, with special reference to their rôle in the lives of animals elementsofbiolog00buch Year: 1933 280 ELEMENTS OF BIOLOGY long (Fig. 191). It is traversed by the blood vessels that connect the placenta with the embryonic circulation and by the stalk of the yolk sac and the stalk of the endodermal structure that in early embry- onic life is the origin of the embryonic portion of the placenta. The PLACENTA UMBILICAL CORD WALL or UTERUS â FOETAL MEMBRANES MOUTH OF UTERUS Fig. 191.âDiagram to show the position of the human foetus in the uter
Elements of biology, with special Elements of biology, with special reference to their rôle in the lives of animals elementsofbiolog00buch Year: 1933 280 ELEMENTS OF BIOLOGY long (Fig. 191). It is traversed by the blood vessels that connect the placenta with the embryonic circulation and by the stalk of the yolk sac and the stalk of the endodermal structure that in early embry- onic life is the origin of the embryonic portion of the placenta. The PLACENTA UMBILICAL CORD WALL or UTERUS â FOETAL MEMBRANES MOUTH OF UTERUS Fig. 191.âDiagram to show the position of the human foetus in the uterus, the umbilical cord, and the position of the placenta. (After Ahlfeld.) large amnionic cavity and the relatively long umbilical cord permit considerable movement of the developing offspring. The amnionic fluid serves to equalize pressure on the embryo and as a protection against contact between the rapidly growing embryo and extra-em- bryonic structures. Embryonic Vestigial Structures. Recapitulation. The adult of higher animals has a considerable number of structures that are
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