The longitudinal fissure is the deep groove down the middle of the brain that separates the left and right cerebral hemispheres. It runs from the front of the brain to the back; the falx cerebri lies inside it, and the corpus callosum, the band that joins the two halves, forms its floor. [1][2][3]
The 3D brain needs JavaScript. The text below still says where the longitudinal fissure is and what it does.
Seen from above and behind, so the brain’s left half is on your left: the left hemisphere’s cortex is lit in blue, the right one’s in orange. The groove is the gap where blue faces orange; the front (coronal) slice button cuts across it. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
A groove has no shape of its own; lit: the parts on either side of it. Lit: on the left, the left hemisphere’s cortex in blue; on the right, the right hemisphere’s cortex in orange. The longitudinal fissure is the deep groove that separates the two cerebral hemispheres, so its two sides are the left and right halves themselves; this model has no shape for the gap, so each half’s cortex (its five lobes and the cingulate gyrus) is lit in its own colour. [1][4]
Not lit: the falx cerebri, the sickle-shaped fold of dura mater that hangs down into the fissure between the hemispheres. The atlas has no shape for it, so the gap is drawn empty. [5][4]
Where it is
It divides the cerebrum into the left and right hemispheres; seen from above, it runs the whole length of the brain from front to back. [3][1]
At the front and the back it splits the two halves completely; in the middle it reaches down only as far as the corpus callosum, the broad band of white matter that connects the hemispheres at the bottom of the fissure. [3][2]
Its walls are the inner (medial) faces of the two hemispheres, and they are folded into gyri and sulci just like the outer surface: the cingulate, parieto-occipital and calcarine sulci all run on these walls. [1][6]
It is a different groove from the central sulcus, which crosses the side of each hemisphere from top to bottom instead of running along the midline. [7]
What it does
A fissure is a deeper furrow than an ordinary sulcus: fissures divide the brain into lobes, and the longitudinal fissure divides it into its two hemispheres. [6]
All three meninges fold down into it. The dura mater between the hemispheres is the falx cerebri, which is attached to the crista galli of the skull at the front and blends with the tentorium cerebelli at the back. [1][5]
Because the meninges fill the gap, no fibres cross between the halves through the fissure itself: tracts joining the left and right cortex pass through the corpus callosum below it. [1]
Two venous channels run along the falx: the superior sagittal sinus in its upper edge, over the fissure, and the inferior sagittal sinus in its free lower edge, arching over the corpus callosum. [5]
Inside it
Cortex lines its walls: the leg area of the primary motor cortex lies close to the midline, folding down into the fissure. [8]
In the human brain two-thirds of the folded cortex is buried within sulci, a figure that counts the cortex hidden inside the longitudinal fissure. [6]
The arachnoid mater stretches across every other sulcus, but in the longitudinal fissure it follows the pia mater down into the gap. [6]
Other names
Also called the great or median longitudinal fissure, the interhemispheric fissure or the cerebral fissure. [1]
Size
The model has no shape for the longitudinal fissure, so the groove itself is not measured here. The stretch where the left hemisphere’s cortex and the right hemisphere’s cortex come within 3 mm of each other fits in a box about 157 mm front to back, 62 mm top to bottom and 4 mm side to side (the box that stretch fits in, not the groove’s length along its bends or its depth). [4]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.