allantois

American  

[uh-lan-toh-is, -tois] / əˈlæn toʊ ɪs, -tɔɪs /

noun

Embryology, Zoology.

1. a vascular, extraembryonic membrane of birds, reptiles, and certain mammals that develops as a sac or diverticulum from the ventral wall of the hindgut.

---

allantois British  

/ ˌælənˈtəʊɪk, əˈlæntɔɪs, ˌælənˈtəʊɪs /

noun

1. a membranous sac growing out of the ventral surface of the hind gut of embryonic reptiles, birds, and mammals. It combines with the chorion to form the mammalian placenta

---

allantois Scientific  

/ ə-lăn′tō-ĭs /

plural

allantoides

1. A membranous sac that grows out of the lower end of the alimentary canal in embryos of reptiles, birds, and mammals. In mammals, the blood vessels of the allantois develop into the blood vessels of the umbilical cord.

---

Other Word Forms

• allantoic
  adjective

Etymology

Origin of allantois

1640–50; < New Latin < Greek allantoeidḗs, wrongly taken for plural and given a singular, on the model of words like hērōís (singular), hērōídes (plural)

Example Sentences

The allantois stores nitrogenous waste and facilitates respiration.

From Textbooks • Jan. 1, 2015

Four embryonic membranes form to support the growing embryo: the amnion, the yolk sac, the allantois, and the chorion.

From Textbooks • Jun. 19, 2013

Some grow to form the extra-embryonic membranes needed to support and protect the growing embryo: the amnion, the yolk sac, the allantois, and the chorion.

From Textbooks • Jun. 19, 2013

During week 3, a finger-like outpocketing of the yolk sac develops into the allantois, a primitive excretory duct of the embryo that will become part of the urinary bladder.

From Textbooks • Jun. 19, 2013

The third is the chorion, forming the outer membrane which encloses the fetus, and within which is the amnion, or innermost membrane which surrounds the fetus, and between which is another membrane, called the allantois.

From What a Young Husband Ought to Know by Stall, Sylvanus