However it may be, we cannot help considering the corpus striatum, from a dynamic point of view, as being indirectly connected with the phenomena of cerebellar activity, and seeing in the superior cerebellar peduncles, in the red ganglions of Stilling, and in the yellowish radii which emerge from them, so many centrifugal conductors, incessantly active foci of nervous radiation, which allow the cerebellar motor influences with which they are charged to overflow into these plexuses.
The cerebellar innervation, is thus intimately asso ciated with the vital phenomena of the corpus striatum as a true auxiliary force. It is incessantly overflowing into its thousand plexuses like a continuous current of electric force, and, as it were, charges its nerve-cells. In motor phenomena it is associated with all our different motor acts, and gives to our movements their regularity, their force, and their continuity. Under a thousand forms, in fact, it silently disperses itself through all the conscious and unconscious actions of the organism, and seems to be an indispensable component of every motor act whatsoever.* 2. The elements of the second group, those which constitute the mass of the efferent fibres of the corpus striatum, are represented by that series of nerve-fibres which are ordinarily described under the name of cerebral peduncles, and which, grouped in the form of isolated fascicles, and arranged in a spiroid fashion, pass in succession, after having traversed the pons, to be dispersed in the different segments of the spinal axis. These fibres, which represent conductors interposed between the different cell-territories of the corpus striatum and the different ganglions of the motor nerves of the spinal chord, are not distinctly isolated at their point of origin in the plexuses of cells of the corpus striatum. (Fig. 6.-12. 17 and 19.) All that we can say of them is, that they appear by insensible degrees in the form of whitish traces creeping over the grey matter of the extra- and intra-ventricular ganglions ; that soon they insensibly increase in volume; that converging like the rays of a fan, they all approach the yellow nuclei of the corpus striatum ; that they gradually enter into contact with the yellow fibres which constitute the substance of these bodies ; and that when, after condensation, they emerge from the corpus striatum, they present themselves in the form of three demi cones, one enclosing the other. (Fig. 6.—I9.)* These nervous elements, having been thus arranged and reinforced by the union of different masses of grey matter belonging to the cerebellar innervation (grey matter of Sommering, grey matter of the pots) (Fig. 6.-18. 19. 19'. 19") pursue a descending and
oblique course, which causes them (on a level with the medulla) to pass insensibly into the opposite regions of the spinal axis. Little by little, and fascicle by fascicle, they separate, to distribute themselves in the different segments of the spinal cord, and in the different groups of motor cells of the antero-lateral regions. These, regularly stratified one above another, like a series of electric machines always ready to start into action, silently await the arrival of the stimulating spark destined to call them into activity.
Thus it follows, from what we have just explained, that the corpus striatum, like the optic thalamus, is a nervous apparatus with multiform activities.
It is a common territory into which the cerebral, cere bellar, and spinal activities come in succession, to be combined, and I might almost say, to anastomose. It thus represents, from a dynamic point of view, a synthesis of multiple elements.
It is in the midst of its tissues that the influence of volition is first received at the moment when it emerges from the depths of the psycho-motor centres of the cerebral cortex. There it makes its first halt in its descending evolution, and enters into a more intimate relation with the organic substratum destined to produce its external manifestations—in one word, materializes itself. (Fig. 6.-12 and 17.) From this moment it comes into intimate contact with the innervation radiating from the cerebellum, and it is now no longer itself, no longer the simple purely psycho-motor stimulus it was at its origin. It is asso ciated with this new influence, which gives it somatic force and continuity of action. It then passes out of the brain by means of the peduncular fibres, combined with a new element, and pursuing its centrifugal course, it is finally extinguished here and there by setting in motion the different groups of cells of the spinal axis, whose dynamic properties it thus evokes. (Fig. 6.-18 and 19.) Thus also, proceeding like an electric current into the different departments it animates, it now tends to produce phono-motor movements designed to express outwardly the emotions of our sentient personality, and now to determine in the different muscular groups, general or partial movements of flexion, extension, or progression, according as it is distributed to such or such groups of satellite cells, the habitual servants of its excito-motor demands.