the natural anatomical foci which preside over the organization and grouping of the cerebral fibres. From a physiological standpoint, the optic thalami are intermediary regions interposed between the purely reflex phenomena of the spinal cord and the activities of psychical life.

By their isolated and independent ganglions they serve as points of condensation for each order of sensorial impressions that finds in their network of cells a place of passage and a field for transformation. It is there that these are for the first time condensed, stored up and elaborated by the individual metabolic action of the elements that they disturb in their passage. It is thence, as from a penultimate stage, that, after having passed through ganglion after ganglion, along the centripetal conductors which transport them, they are launched forth into the different regions of the cortical periphery in a new form-intellectualized in some way, to serve as exciting materials for the activity of the cells of the cortical substance. (Fig. 6—14. 9. 4.)

These are, then, the sole and unique open gates by which all stimuli from without, destined to serve as pabulum vitæ for these same cortical cells, pass; and the only means of communication by which the regions of psychical activity come into contact with the external world.*

* From the intimate connexions which unite the plexuses of the optic thalamus with those of the cortical layer, and which cause these latter, as regards the evoking of their activity, to be completely dependent upon the materials transmitted to them, it may be understood what an important part the morbid activity of the plexuses of the optic thalami may play in the evolution of various hallucinatory processes. See, for complementary details on the importance of irritations of the optic thalami in the development of hallucinations, the inaugural thesis of Dr. Ritti. Paris, 1874.

On the other hand, a direct examination of the relations of the centres of the optic thalami to the different regions of the cortical periphery enables us to determine the following peculiarities also.

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 visu, throw a completely new light upon that longdiscussed 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

* See my "Inconographie photographique des centres nerveux." v. vi.

Plates iv.

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 richness 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 temperament 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 such or such a group of sensorial impressions, which find in the regions of psychical activity in which they are particularly 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 * The experiments of Schiff tend to show that the vascular nerves of the liver and stomach pass over the medulla oblongata to terminate higher up. "A portion of them," he says, 'appears to reach the optic thalamus." ("Compte rendu de l'académie des sciences," 15th Sept., 1862.)

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 peculiar 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.

CHAPTER V.

THE CORPUS STRIATUM.*

THE mass of grey matter designated by the name of corpus striatum is the complement of the optic thalamus, with which it constitutes those two grey ganglions which occupy the central region of each hemisphere, and which are, as has been frequently pointed out, the natural poles around which all the nervous elements gravitate.

While the optic thalami present, in a manner, masses of grey matter grouped around the prolongation of the posterior columns of the spinal axis, of which, speaking in general terms, they form the crown, the corpora striata are, on the contrary, situated on the prolongation of the antero-lateral columns. They therefore evidently occupy an anterior situation as regards the optic thalami; and in connection with this subject, it is not without interest to remark that the same relations that exist in the whole of the spinal cord, are here reproduced with obviously analogous characteristics.

In the cord the sensitive or excito-motor regions occupy the posterior portion, while the essentially motor regions occupy the anterior.

In the brain the same relations as to neighbourhood,

* Fig. 6, p. 61, and Fig. 5, p. 31.