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A fluid-filled sac- or sausagelike, extraembryonic membrane lying between the outer chorion and the inner amnion and yolk sac of the embryos of reptiles, birds, and mammals. It is composed of an inner layer of endoderm cells, continuous with the endoderm of the embryonic gut, or digestive tract, and an outer layer of mesoderm, continuous with the splanchnic mesoderm of the embryo. It arises as an outpouching of the ventral floor of the hindgut and dilates into a large allantoic sac which spreads throughout the extraembryonic coelom. The allantois remains connected to the hindgut by a narrower allantoic stalk which runs through the umbilical cord. See Amnion, Chorion, Germ layers

The allantois eventually fuses with the overlying chorion to form the compound chorioallantois, which lies just below the shell membranes in reptiles and birds. The chorioallantois is supplied with an extensive network of blood vessels and serves as an important respiratory and excretory organ for gaseous interchange. The allantoic cavity also serves as a reservoir for kidney wastes in some mammals, in reptiles, and in birds. In the latter two groups the allantois assists in the absorption of albumin. In some mammals, including humans, the allantois is vestigial and may regress, yet the homologous blood vessels persist as the important umbilical arteries and veins connecting the embryo with the placenta. See Fetal membrane, Placentation


A fluid-filled, saclike, extraembryonic membrane lying between the chorion and amnion of reptilian, bird, and mammalian embryos.
References in periodicals archive ?
The chapter 5 summarizes allantoic acid prices data.
A simple umbilical pseudocyst requires no treatment, but needs to be differentiated from an allantoic cyst with persistent patent urachus.
None of the nasal /ocular swabs and allantoic fluid samples collected from chicken embryos inoculated with samples from Farm Nos.
This observation is interesting, because some authors recommend testing the allantoic fluid for hemagglutination activity only from dead embryos.
Embrex is developing and commercially testing the world's first automated prototype device that detects estrogenic compounds in the allantoic fluid of embryonated eggs.
The tracheal aspirate specimen was inoculated on monolayers of MDCK cells and into the allantoic cavities of 10-day-old embryonated chicken eggs.
We attempted to isolate the virus by injecting the chorioallantoic membranes (CAM) and allantoic cavities of 9-day-old specific pathogen free (SPF) chicken embryos with the scab specimens that were positive for FWPV.
Samples that showed a positive reaction in the partial M segment RT-PCR were grown in the allantoic cavities of 10-day-old specific pathogen-free embryonated chicken eggs.
Allantoic fluid was harvested 36 h postinfection and tested for HA with chicken erythrocytes to confirm virus isolation (8).
50]) of pooled allantoic fluid containing A/Anhui/1/2013 (H7N9) in 100 [micro]L of phosphate-buffered saline.
Allantoic fluid from the injected eggs agglutinated 0.