The septum pellucidum (Latin for "translucent wall") is a thin, triangular, vertical double membrane separating the anterior horns of the left and right lateral ventricles of the brain.

The septum pellucidum is located in the septal area in the midline of the brain between the two cerebral hemispheres.

It is attached to the lower part of the corpus callosum, the large collection of nerve fibers that connect the two cerebral hemispheres.

[1] During fetal development, there is a space between the two laminae called the cave of septum pellucidum that, in ninety percent of cases, disappears during infancy.

[5] Absence of the septum pellucidum occurs in septo-optic dysplasia, a rare developmental disorder usually characterized by abnormal development of the optic disk and pituitary deficiencies.