rugae (n.)

plural of ruga (1775), from Latin ruga "a wrinkle in the face," from Proto-Italic *rouga-, which is of uncertain origin. "Since words for 'wrinkle' and 'crease' are often derived from 'to be rugged', from which also 'to belch' is often derived ..., the most obvious connection is with e-rugere 'to belch'" [de Vaan].