pineal gland

synonym: epiphysis
https://doi.org/10.1351/goldbook.11092

Pea-sized conical mass of tissue behind the third ventricle of the brain, secreting the hormone-like substance melatonin in some mammals.

Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 792 [Terms] [Paper]