An embryonic appendage, the allantois, used in reptiles and birds for respiration, has here been turned to another purpose.
The function of the allantois is still in a great measure unknown.
The arteries of the allantois are originally the terminations of the primitive aort.
The cavity of the allantois, if developed, vanishes completely.
The allantois becomes a part of the fetal umbilical cord after the formation of the placenta.
Similar movements are also seen in the allantois at a considerably later period.
The other part of the archenteron wall make the allantois, the hind gut and the bladder.
It thus comes about that the further splitting of the mesoblast merely enlarges the cavity in which the allantois lies.
The fasciculus attached to the embryo is the allantois which becomes the umbilical cord.
As the allantois increases in size and importance, the allantoic vessels are correspondingly developed.
allantois al·lan·to·is (ə-lān'tō-ĭs)
n. pl. al·lan·to·i·des (āl'ən-tō'ĭ-dēz')
A membranous sac that develops from the posterior part of the alimentary canal in the embryos of mammals, birds, and reptiles, and is important in the formation of the umbilical cord and placenta in mammals. Also called allantoid.