Pertumbuhan pada bagian ventral dari embrio reptil, burung, dan mamalia. Pada manusia merupakan sisa pertumbuhan kecuali pembuluh darahnya membentuk tali pusat. Kata sifat: allantoic.

Merriam-Webster Online Dictionary
allantois (noun)
a vascular fetal membrane of reptiles, birds, and mammals that is formed as a pouch from the hindgut and that in placental mammals is intimately associated with the chorion in formation of the placenta
Allantois (Wikipedia)
Diagram illustrating early formation of allantois and differentiation of body stalk
Sectional plan of the gravid uterus in the third and fourth month
Days 16
Precursor yolk sac
Gives rise to Umbilical cord
Latin Aallantois
MeSH A10.615.284.147
Code TE E6.
Anatomical terminology

The allantois (/əˈlæntɔɪs/; plural allantoides or allantoises) is a sac-like structure that forms part of a developing amniote's conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.

The allantois, along with the amnion and chorion (other embryonic membranes), identify humans, and other mammals, as amniotes. Other amniotes include reptiles, dinosaurs, and birds. Of the vertebrates, only Ichthyopsidas (fish and amphibians) lack this structure.