As this column passes onward in the medulla oblongata, on a level with the glosso-pharyngeal nerve, it forms a group of cells of large size. Besides numerous other connections which it forms, Clarke describes the motor root as sending processes forward, like tapering brushes or tails of fibres, in connection with more scattered cells lying in their course, which may be frequently seen to communicate with the transverse bundles which traverse the "gray tubercle" and the sensory roots of the fifth contained therein. In this way the sensory root, though seemingly much separated from, is really in very direct connection with, the motor root. Now, proofs, which must be considered almost positive, have recently been adduced to show that the nerve-fibres concerned in those peculiar alterations in the tissues supplied by the ophthalmic division of the fifth, which occur in section of the trigeminus, come entirely from the motor root of the fifth, and form a very small band in the inner or medial margin of the ophthalmic trunk. The observation of Meissner[21] goes to show that it is possible (by good luck) to divide the trunk in such a partial manner as to cut only the inner fibres, and thereby produce the trophic eye-changes without any anæsthesia, or only the sensory fibres, and thereby induce anæsthesia without any trophic changes; and it must be owned that this really affords the only reasonable explanation of the discrepancy between the experimental results obtained by Magendie and Bernard; and also the facts of such cases as those related by Mr. Hutchinson,[22] who in two instances found that a completely anæsthetic eye recovered perfectly well from the wound made in a surgical operation. The nature of the nervous influence (whether ordinary vaso-motor only, or a special trophic function) has been greatly disputed. Dr. Wegner,[23] from observing the remarkable group of glaucomatous cases under Horner (of which one has been related), made experiments, from which he concluded that the augmentation of intra-ocular pressure in glaucoma was a phenomenon dependent upon the sympathetic, which was irritated by reflection from the trigeminus. But the researches of Hippel and Grunhagen, especially their latest,[24] give a different explanation, excluding the sympathetic; they found that irritation of the medulla oblongata, in the neighborhood of the trigeminus root, produced a lasting and very pronounced augmentation of intra-ocular blood-pressure, an effect which, they remark, could not depend on irritation of the vaso-motor centre, since that must produce contraction of the vessels and lowering of the blood-pressure. They conclude that "the trigeminus contains specific fibres which possess the property of actively dilating the blood-vessels of the eye;" and in reference to the secretion of the fluid humors of the eye, they conclude also that "the trigeminus also plays the part of an (active) nerve of secretion."