Plural of fornix; archways or vaults, especially the curved structures in Roman architecture or anatomy.
From Latin fornix (arch, vault, tunnel), which became the plural fornices. In anatomy, it refers to the arch-shaped structures in the brain and elsewhere, named for their resemblance to architectural arches.
The human brain has structures called fornices that look like little arches—so anatomists borrowed the Roman word for architectural vaults to describe the brain, meaning your neurons are living under ancient buildings!
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