The fundamental root zone lies upon the outer side of the direct pyramidal tract in the cord, and in the medulla as far as the lower extremity of the olive, where it passes inwards beneath the the anterior pyramid between the olive and the raphe. Above the olive, it spreads out into a thin layer of fibres which crosses the fillet obliquely in an outward direction to the upper border of the middle peduncle of the cerebellum, where it becomes superficial upon the anterior part of the outer surface of the superior peduncle, or pro census, and terminates in the testes and brachium posterius. These tracts, one on each side, might with propriety be called the posterior peduncles of the corpora quadrigemina, and it is probable that through them, movements of the body, and the maintenance of the equilibrium, are directed by vision. Possibly it is the function of the nates to direct the move ments of the eyes to accommodate the vision to the attitudes of the body and the movements of an object, and of the testes to regulate the actions of the muscles to avoid a blow or to grasp an object.
The fundamental root zones, the corpora quadrigemina, brachia, corpora geniculata, the grey matter around the iter and the optic tracts together constitute a visual reflex system.
The anterior root zone, on either side, is divided from the fundamental root zone by the anterior roots of the spinal nerves. It joins the fillet of the Pons, in which it lies between the olivary fasciculus in front, and the fillet fibres derived from the floor of the fourth ventricle, behind. In the emus cerebri, the fillet is internal to the crusts, from which it is separated by the snbstantia nigra. In the crus, it is related internally below with the processus of the same side previous to its decussation, and higher up, with the pro cessus of the opposite side subsequent to its decussation, and, with the red nucleus of the tegmentum. In the internal cap sule the fillet crosses the internal surface of the motor tract in an oblique direction, beneath the thalamus, and in front, lies in a broad groove on the anterior margin of the internal capsular fibres of the crusts. It terminates with the fillet fibres derived from the thalamus in the frontal lobe of the cerebrum.
As the fillet passes upward from the pops Varolii receives accessions from various ganglia, and a great mass from the thalamus, which unite with it to form the anterior division of the internal capsule. The longitudinal commissures of the cerebrum unite with the fillet in the anterior lobes of the brain, and with it constitute the fillet system. There is evi
dence to support the theory, that the fillet is the perceptive system through which the mind is made acquainted with its environments; and, through the medium of the longtudinal commissures, with the memories of things and the events of the past, which have been laid up in the temporal and occipital lobes of the brain.
The direct cerebellar tract of the spinal cord originates iu the vesicular column of Clarke, occupies the outer side of the cord, medulla and restiform body, and with the latter passes into the cerebellum. It probably assists in the formation of a cerebello-spinal system, which is concerned in the function of nutrition.
The posterior median columns are continued in the me dulla by the posterior pyramids, and terminate in the clavate nuclei, beyond which their connections are uncertain. If these columns are respiratory tracts, as supposed by some au thorities, they probably form an arc with the fifth aud pueumo gastric nerves, through which the muscles of respiration are co-ordinated and brought into action. Until corrected, we will class this tract and its associations as a respiratory system.
The posterior root zone, or Burdach's column, lies external to the posterior median column, and behind the posterior born of the grey matter of the cord and the lower half of the medulla. This column terminates above in the restiform nucleus, and is continued by the restiform body to the dentate nucleus of the cerebellum. It is associated bY the corpus dentatum 1-vith the cerebellum behind, and above, by the pro cessus with the opposite red nucleus, thalamus, and hemis phere of the cerebrum. The association formed by this tract in conjunction with the cerebellum, and the temporal and occipital lobes of the cerebrum, including the intermediate tracts and grey masses, constitutes the organic and memory system.
Thus the columns of the spinal cord are associated into six systems, having distinct functions, which are co-Ordinated at various points by vesicular masses that unite the several systems into one great function, comprehended in the word mind.
The reader is here cautioned against accepting, without due reflection and investigation, the theories advanced in rela tion to the function of the tracts described and associated into systems. This has been done for the purpose of assist ing the memory in retaining the anatomical relations.