Anatomical funnel-shaped opening, often referring to the hollow stalk that connects the hypothalamus and the posterior pituitary gland, or to the portion of the Fallopian tube that receives the ovum.
Source: PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 769 (https://doi.org/10.1515/pac-2015-1202)