ALLANTOIS

(Gr. aXkas, a smisage, and li , form.] A thin membranous sac developed from the termination of the alimentary canal of the embryo, situated between the amnion and chorion, and organised by the hj arteries and umbilical vein. Its functions, as a re organ, is of most importance in those oviparous vertebrates where the embryo has no branchiae: in the mammal i a,itsuse is more or le superseded by the chorion and placenta. In some quadrupeds the allantois has the form of a sausage; whence its name. [s. 46]