Membranous labyrinth includes cochlea and vestibular apparatus (saccule + utricle + 3 semicircular canals). Corpus callosum is a tract of nerve fibres by which the hemispheres are connected with each other. Myelinated nerve fibres are commonly found in CNS and are far more common than non-myelinated neurons. In PNS (peripheral nervous system), spinal and cranial nerves also have myelinated nerve fibres. Pigments in photoreceptors - Rhodopsin (or visual purple) in rods and iodopsin (or visual violet) in cones.