See navel.
Biology A small opening or depression similar to a navel, as the hollow at the base of the shell of some gastropod mollusks, one of the openings in the shaft of a feather, or the hilum of a seed.
umbilicus um·bil·i·cus (ŭm-bĭl'ĭ-kəs, ŭm'bə-lī'kəs) n. pl um·bil·i·ci (-sī') See navel.