What does "fissure" mean?

Fissure: A narrow opening, made by the parting of any substance; a cleft; as, the fissure of a rock. Cerebral fissures (Anat.), the furrows or clefts by which the surface of the cerebrum is divided; esp., the furrows first formed by the infolding of the whole wall of the cerebrum. -- Fissure needle (Surg.), a spiral needle for catching together the gaping lips of wounds. Knight. -- Fissure of rolando (Anat.), the furrow separating the frontal from the parietal lobe in the cerebrum. -- Fissure of Sylvius (Anat.), a deep cerebral fissure separating the frontal from the temporal lobe. See Illust. under Brain. -- Fissure vein (Mining), a crack in the earth's surface filled with mineral matter. Raymond.