IT IS known that dorsal root neurons conducting different types of sensation run a different course after entering the spinal cord and terminate in different nuclei. Knowledge of the exact course of pathways for the several modalities of sensation, however, is still fragmentary. A wide gap remains especially between the primary sensory root neurons and the better known longer central pathways containing the secondary sensory neurons. It is not known exactly on which ganglion cells the dorsal root fibers subserving different functions terminate and whether this second group of ganglion cells contribute fibers to the long ascending tracts or internuncial ganglion cells with a short axon deliver the sensory impulses to a third group of neurons, with a longer axon. Especially defective is information concerning the exact termination of neurons within the spinal cord and the brain stem which belong to receptors situated in different parts of the sensory segment,