The cortex (gray matter) of the cerebral hemispheres is known as neocortex and has six indistinct layers. Beneath the pia-arachnoid there is an outer plexiform layer with nerve cells arranged horizontally. Next is the outer granular layer containing small pyramidal neurons. Next is the outer pyramidal cell layer with medium-sized pyramidal neurons. Below this is the inner granular layer of larger pyramidal neurons. Beneath this is the inner pyramidal layer of larger pyramidal neurons. The innermost cortical layer is the polymorphous layer that lacks pyramidal cells. Beneath the cortex is the white matter.