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
Choroidal fissure Choroidal fissure The choroid is the middle, vascular coat of the eye which resides between the sclera and the retina. Early in development the choroidal fissure is a groove that extends along the ventral aspect of the optic stalk. In effect, it is a continuation of the invagination that forms the optic cup during early development in amniotes. For a period of time this groove extends to the closing lips of the optic cup. During development it is through the choroidal fissure that the retinal vessels enter and leave the eye. While optic neural components (e.g. axons arising from retinal