antrum

https://doi.org/10.1351/goldbook.10414
Cavity or chamber, often in bone, with specific meanings in some hollow organs (e.g., the pyloric end or gastric antrum of the stomach).
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 725 [Terms] [Paper]