"Air sac" and "air cell" in a chicken embryo I need to translate the Russian term "воздушный мешок". It is part of the chicken embryo, marked by number 5 in the figure below. > ![enter image description here]( I found the expression **air cell** but also found the expression **air sac** in English. On one site, "air sac" is described as a synonym to the "allantoic sac": >  so as to apply the material onto the chorioallantoic membrane (CAM).

According to Atlas of Chick Development by Ruth Bellairs and Mark Osmond, a book I'm using for my developmental biology course :

> **Air space** is the space between the two shell membranes at the blunt end of the egg. The chick pushes its beak into this space shortly before hatching and takes its first breathe of air.

Besides allantois is the extra embryonic membrane and the space enclosed by it is allantoic cavity.

Here label **2** is Allantoic cavity.