Some volcanoes exhibit lateral and fissure eruptions. Also absent was part of a bordering region called the lateral sulcus (Sylvian fissure). In the medial part of the medulla is the anterior median fissure. The vessel is placed in the pia mater along the anterior median fissure. It is the indented area medial to the pterygomaxillary fissure leading into the sphenopalatine foramen. Complications from constipation may include hemorrhoids, anal fissure or fecal impaction. A fracture will sometimes form a deep fissure or crevice in the rock. It is sometimes confused with the medial longitudinal fissure. This deprives resident plaque bacteria of carbohydrate, preventing the formation of pit and fissure caries. The upper, horizontal fissure, separates the upper from the middle lobe. Laki, a volcanic fissure in the south of the island, erupted. The island is of volcanic origin, mostly made of fissure vents. Photographs of the brain show an enlarged Sylvian fissure. This occurs along the parieto-occipital fissure (yellow in figure). It can be used to divide the regions of the superior orbital fissure.