The present report describes the results of experiment designed to study supraspinal systems in the American opossum by several techniques. The data indicate that although spinal fibers from the opossum motor-sensory cortex are small and limited in their distribution, those from the brain stem are comparable in their origin, course, caudal extent and distribution to those described for placental mammals. Such results support the use of the opossum as an experimental animal for nervous system research; but, furthermore, suggest that its marsupial embryology makes it an ideal model for experiments designed to elucidate the ontogeny of the nervous system.