Phys. [mod. L. in form, a factitious sing. f. the earlier form allantoīdes, ad. Gr. ἀλλαντο-ειδής: see ALLANTOID.] The fœtal membrane (so named by ancient anatomists from its form in a calf) found only in mammals, birds, and reptiles, which lies between the amnion and chorion, and forms a means of communication between the fœtal and maternal blood.
1646. Sir T. Browne, Pseud. Ep., 270. The Allantois is a thin coat seated under the Corion, wherein are received the watery separations conveyed by the Urachus.
1691. Ray, Creation (1701), 82. Abundance of urine in the Allantoides.
1879. Syd. Soc. Lex., s.v., [In birds] by its proximity to the shell, the allantois is an important respiratory organ.
