A sulcus is a shallower groove that surrounds a gyrus. A fissure is a large furrow that divides the brain into lobes, and also into the two hemispheres as the medial longitudinal fissure does.[1] However this distinction is not always clear. For example, the lateral sulcus is also known as the lateral fissure or the Sylvian fissure, and the central sulcus is also known as the central fissure or the Rolandic fissure.