What is the X in X-mas?
plural sulci, Latin, literally "furrow, trench, ditch, wrinkle."
sulcus sul·cus (sŭl'kəs)
n. pl. sul·ci (-kī, -sī)
Any of the grooves on the brain surface, bounding the gyri; a fissure.
A long narrow groove or depression, as in an organ or a tissue.