Definition of Fornix

Fornix: In anatomy, a vaultlike or arched structure.

For example:

• The fornix in the brain -- a fibrous arching band connecting the two lobes of the cerebrum.
• The fornix of the conjunctivae -- loose arching folds connecting the conjunctival membrane lining the inside of the eyelid with the conjunctival membrane covering the eyeball.
• The fornix of the vagina -- the anterior (front) and posterior (back) recesses into which the upper vagina is divided. These vaultlike recesses are formed by protrusion of the cervix into the vagina.

"Fornix" is the Latin word for "vault or arch." "Fornix" is closely related to "fornication." It seems that prostitutes in ancient Rome used to hang out under the arches of certain public buildings. The act of carrying on an illicit sexual relationship consequently came to be called "going under the arches" or fornication.