AbstractThe results of the previous experiments confirm May and Horsley's conclusions that the mesencephalic trigeminal root contains both ascending and descending fibers. The former take origin from sensory cells in the semilunar ganglion and the latter from globular, unipolar cells in the alar (sensory) plate of the mesencephalon, and from a caudal continuation of these cells, known as the locus. coeruleus, which extend downward into the motor area of the pons.