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The longitudinal fissure is a long, deep cleft that extends along the entire length of the human brain and divides it into right and left hemispheres. It's known by several names, including the great longitudinal fissure, the medial longitudinal fissure, the longitudinal cerebral fissure, and the interhemispheric fissure. This cleft is covered by the falx celebri, a fold of the dura mater that is the outermost layer of protective tissue that covers the brain and spinal cord.
This fissure is part of the cerebral cortex, also called the cerebrum, which is the outermost layer of neural brain tissue. In humans and other large mammals, the cerebral cortex is a folded structure consisting of many ridges and grooves. Approximately two-thirds of the human brain is buried in such grooves. The top layer of the cerebral cortex is a type of neural tissue called gray matter, and the inner layer is called white matter. The entire structure of the cerebral cortex is divided into four pairs of lobes.
Portions of three out of the four paired lobes of the brain border and extend down into the longitudinal fissure. These are the frontal lobes, which are located at the front of the brain, the parietal lobes at the top and upper sides of the brain, and the occipital lobes, which are found at the back of the brain. The fourth pair are called the temporal lobes and are located on the lower sides of the brain in what is commonly called the temple region and extend back behind the ears.
The corpus callosum is located beneath the longitudinal fissure, separating it from deeper brain structures. It's a thick flat bundle of neural fibers and is the largest white matter structure in the human brain. Interhemispheric communication is made possible by the corpus callosum, which connects the two brain hemispheres.
The cerebral falx, which is also known as the falx cerebri, is the dural tissue that covers and protects the area. The term dural tissue refers to the dura, also called the dura mater, which is a type of meningeal tissue. Collectively called the meninges, there are three layers of meningeal tissue, each of which can be further subdivided into more layers. The bottom meningeal layer is called the pia mater, the middle and most delicate layer is the arachnoid mater, and the topmost layer is the dura mater, which is often described as tough or leather-like indicating its protective function.