Multinucleate striated contractile fibers which exhibit differentiation markers characteristic of skeletal muscle develop regularly in optic nerve cultured from 10-day-old rats. In identical conditions, muscle fibers arise also from pineal and occasionally from spinal cord, but not from meninges, cerebral blood vessels, trigeminal nerve, nor brachial plexus. These observations are consistent with the suggestion that mammalian cephalic neuroectoderm has myogenic potential. The concept that skeletal muscle in different anatomical regions might have different embryonic origins could be relevant to the distribution of muscles affected by certain diseases in man.