Longitudinal fissure Longitudinal fissure The longitudinal fissure (or cerebral fissure, median longitudinal fissure, or interhemispheric fissure) is the deep groove that separates the two hemispheres of the vertebrate brain. The medial surfaces of the two hemispheres are as similarly convoluted by gyri and sulci as is the outer surface of the brain. It is thought that a majority of existing animals, including Homo sapiens, have evolved from a common wormlike ancestor that lived around 600 million years ago, called the urbilaterian. A bilaterian animal is one that has symmetrical left and right body halves. While it is still debated whether this species
Anterior median fissure of spinal cord Anterior median fissure of spinal cord The anterior median fissure of the spinal cord has an average depth of about 3 mm, but this is increased in the lower part of the spinal cord. It contains a double fold of pia mater, and its floor is formed by a transverse band of white substance, the anterior white commissure, which is perforated by blood vessels on their way to or from the central part of the medulla spinalis. The anterior median fissure provides a groove in which the anterior spinal artery sits. From here, it provides the anterior part of the