Their precise origin in the different regions of the cortical periphery is still a problem to be solved for each of them in particular. (Fig. 6-6. 1 i. 16.) This is also the case as regards their central distribution in the different cell-territories of the corpus striatum. (2. 12. 17—Fig. 6.) At the present day they are only known and anatomically demonstrable in an intermediate por tion of their transit, at the moment when they are reflected in the form of serpentine fibres ;* and yet their existence, as centrifugal conductors of motor stimuli, radiating from the excitable zones of the cere bral cortex, is very clearly demonstrated. This is one of the most interesting points that experimental physio logy has brought to light in recent times.
The recent researches of Fritsch and Hitzig, who were the first, in 1870, to point out that certain zones of the grey cortex were excitable by galvanic currents,t have opened the road in this direction.t Ferrier has shown, indeed, after them, that by applying electric excitement in such or such a region of the grey cortex, motor reactions in such or such isolated groups of muscles are determined ; that at will we may cause the eyes, tongue, neck, etc., of an animal to move, according as we electrify such or such a convolution ; and that, in a word, there are in the tissue of the cortical layer a series of small independent motor centres, which may be isolatedly excited, and which communicate by independent conductors with the different portions of the muscular system. More than this, it has been proved that things take place in the same manner in man ; for an American physician, pushing the boldness of experiment to its ultimate limits, obtained similar results in a patient whose brain was denuded by a degeneration of the cranial case.§ Finally, in certain pathological cases in which I made special researches, still unpublished, I have even been able to demonstrate, as a proof of the exist ence in the cortical layer of isolated foci of motor excitation, that in persons who had undergone amputa tions at a distant date—subjects who had been long deprived of an upper limb, in the case of disarticulation of the shoulder, for instance—there existed in certain long disused regions of the brain, coincident, very dis tinctly localized atrophies. I have, moreover, demon strated that the atrophied regions of the brain are not the same in the case of the amputation of a leg, and in that of amputation of the upper limbs.
These facts, then, as I have already explained in former works, already extending over ten years, authorize us to conclude that there exists a special order of nerve-fibres radiating from different departments of the cortical substance, and distributed in isolated territories of the grey matter of the corpus striatum, which is thus associated as a co-operant factor in all the vibra tions that take place in the plexuses of cerebral cells ; and to consider it as proved that these different groups of cortico-striate fibres have each an independent point of origin.
j3. The afferent of the second group, as we have already indicated, are represented by the terminal expansions of the cerebellar peduncles.
The superior cerebellar peduncles, in fact, after inter crossing in the median line, become associated and form two masses of grey matter, described by Stilling, and recognizable by their reddish colour.
These two ganglions, which, as regards their structure and connections represent a veritable focus of radiation for cells and nerve-fibres, give rise throughout all their antero-external substance to a series of fibrils, inter laced in a thousand ways, which all terminate in the form of yellowish filaments, in the grey matter of the corpus striatum. It is this special contingent—an in direct emanation from the active elements of the cere bellum—that gives to this particular department of the corpus striatum, that characteristic yellowish colour, which I have already described under the name of the yellow nucleus of the corpus striatum.
These fibrils of cerebellar origin which are disposed in the form of yellowish rayed filaments, taper away insen sibly, and embrace the white spinal fibres which expand in the corresponding regions of the corpus striatum ; and are probably lost in the network of large cells, as has been previously suggested.
Now, how do they terminate ? What is the ultimate mode of combination of the individual elements which represent in the brain the activity of the cerebellum ? How does the cell of the corpus striatum come into contact with the cerebellar elements of the new importation ? So far I have only been able to form conjectures, and while supposing that there must be some sort of ana tomic combination between these elements of varied origin, I can only pause and await the results of future researches.