Anatomical peculiarity of Mormyridae. The anterior portion of the cerebellum, the valvula cerebelli, as in other teleostei is enclosed inside the mesencephalon, it actually fills the 3d brain ventricle, the ventriculus mesencephalicus. But due to its size (it is also called gigantocerebellum ), it pushes aside the lobi optici of the tectum opticum, the site of the visual centre in lower vertebrates. Its size in unique in the Mormyridae, in Gymnarchus the valvula is somewhat enlarged, but not as big as in Mormyridae. In the other Osteoglossomorpha the brain is not particularly different from that of other fishes.