Sulcus (morphology)

In biological morphology and anatomy, a sulcus (pl. "sulci") is a furrow or fissure. It may be a groove in the surface of a limb or an organ, notably in the surface of the brain, but also in the lungs, certain muscles (including the heart), as well as in bones, and elsewhere. Many sulci are the product of a surface fold or junction, such as in the gums, where they fold around the neck of the tooth.
In invertebrate zoology, a sulcus is a fold, groove, or boundary, especially at the edges of sclerites or between segments.