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
Precentral gyrus contralateral side of the body (facial palsy, arm-/leg monoparesis, hemiparesis) - see upper motor neuron. Precentral gyrus The precentral gyrus (also known as the motor strip) is a prominent structure on the surface of the posterior frontal lobe. It is the site of the primary motor cortex (Brodmann area 4). The precentral gyrus lies in front of the postcentral gyrus - mostly on the lateral (convex) side of each cerebral hemisphere - from which it is separated by the central sulcus. Its anterior border is represented by the precentral sulcus, while inferiorly it borders to the lateral fissure ("Sylvian fissure").