It is sufficient to cast a glance over horizontal sections of the brain to recognize that each of these centres is more particularly in connection with certain regions of this very cortical substance. Thus, for instance, we see plainly that the central ganglion, by means of the white fibres that emerge from it, apparently radiates the impressions it condenses towards the antero-lateral regions of the brain,* and that the posterior centre acts in the same manner as regards the regions of the posterior cornua ; while the median centre, by means of the divergent fibrils which are implanted in its 'mass, appears to direct its radiations indifferently towards all parts of the cortical substance. The anterior centre, less distinctly attached to the cortical substance, seems, nevertheless, to have its special area of distribution in the grey matter of the hippocampus. In the animal species in which the olfactory organs are well developed, this convolution similarly exhibits a high degree of development.
These anatomical data, which every one can observe, de visit, throw a completely new light upon that long discussed question as to cerebral localizations, and are direct evidence that there are in the different regions of the cortical substance isolated circumscribed localities, affected in an independent manner, for the reception of such or such kinds of sensorial impressions. We are thus logically led to comprehend that the peripheral development of such or such a sensory organ is designed to have a receptive organ in some way adapted to it in the central regions, and that the rich ness in nerve-elements of such or such a region of the cortical substance itself, and the degree of proper sensibility and specific energy of each of them, may, at a given moment, play an important part in the sum total of mental faculties, and thus determine the tem perament of the specific activity of such or such an organization.
We thus recognize the fact that the secret of certain aptitudes—of such or such a native predisposition, is naturally derived from the preponderance of sul or such a group of sensorial impressions, which find in the regions of psychical activity in which they are particu larly elaborated a soil ready prepared, which amplifies and perfects them according to the richness and degree of vitality of the elements placed at their disposal.
Finally, the plexuses of the central grey matter, which are similarly united to the different regions of the cortical substance, show us that stimuli radiated from the depth of visceral life ascend, with the organic tissue which carries them, as far as the interior of the brain* (the experiments of Schiff confirm this) ; and that they are thus carried into the different regions of the cortical substance, and associated with the essential phenomena of psychical activity.
From this double induction we are therefore led to consider the masses of grey matter, usually described under the name of optic thalami, as essentially central regions which are the bond of union between the various elements of the entire cerebral system.
Through their tissues pass vibrations of all kinds, those which radiate from the external world, as well as those which emanate from vegetative life. There, in the midst of their cells, in the secret chambers of their pecu liar activity, these vibrations are diffused, and make a preparatory halt ; and thence they are darted out in all directions, in a new and already more animalized and more assimilable form, to afford food for the activity of the tissues of the cortical substance, which only live and work under the impulse of their stimulating excite ment,