The longitudinal fissure, also called the interhemispheric or great longitudinal fissure, is a deep cleft that divides the cerebrum into two cerebral hemispheres. It is a prominent feature in most vertebrate brains and is particularly well developed in mammals. The fissure runs along the midline of the brain and exposes the medial surfaces of each hemisphere, making visible a number of important structures associated with midline anatomy. For general context on vertebrate brains see vertebrates and for the cerebrum see cerebrum. The paired halves are commonly referred to as cerebral hemispheres and together form the largest portion of the human brain.
Anatomy and neighboring structures
Within the fissure lie layers of meninges and vascular channels. The falx cerebri, a sickle-shaped dural fold, descends into the fissure and helps separate the hemispheres; see falx cerebri. The superior sagittal sinus runs in the attached margin of the falx and receives venous blood from bridging veins. Arachnoid membrane spans the fissure, and cerebrospinal fluid occupies the subarachnoid space. Deep beneath these coverings, bundles of commissural fibers — most notably the corpus callosum — provide the principal connections that allow the two hemispheres to communicate.
Development and variation
The fissure forms as the cerebral hemispheres expand and separate during embryological development of the forebrain. Its depth and appearance vary between species and among individuals. Certain congenital conditions, such as agenesis of the corpus callosum, can alter the relationship between the hemispheres and the fissure’s mediating structures. Minor asymmetries in the fissure and in hemispheric anatomy are common and often correlate with functional lateralization.
Function, clinical relevance and surgical access
Functionally the fissure itself is a structural divider rather than a processing center; its importance lies in the arrangement and protection of midline elements and in providing surgical corridors. Neurosurgeons often approach medial frontal or deep-seated lesions via interhemispheric routes that traverse the fissure. Radiologic imaging routinely shows the fissure and adjacent anatomy when evaluating trauma, tumors, midline shifts, or venous thrombosis in the superior sagittal sinus. Procedures such as corpus callosotomy intentionally interrupt commissural fibers to reduce seizure propagation in selected forms of epilepsy.
Notable facts and distinctions
- The term "longitudinal fissure" emphasizes its extension along the brain’s long axis; "interhemispheric fissure" highlights its role separating two hemispheres.
- Although the fissure separates the hemispheres, multiple commissures — corpus callosum, anterior commissure and others — maintain interhemispheric communication.
- Visible anatomy in the fissure, such as the falx and venous sinuses, is important in both neurosurgery and diagnostic imaging.
For further anatomical and clinical details consult specialized neuroanatomy resources and surgical texts that discuss interhemispheric approaches and midline cerebrovascular anatomy. Additional introductory information can be found under entries for vertebrates, cerebrum, cerebral hemispheres, human brain and falx cerebri.