In a case reported by Serres, in a man who had suddenly lost the sight of both eyes, they found on autopsy a effusion occupying the optic thalamus on a level with the grey commissure, that is to say on a level with the middle centres.
In two unpublished cases observed by myself, I noticed a loss of sensation on one side of the body, coincident with an isolated destruction of the median centre of the opposite side.
Finally I have twice observed, in the brains of two deaf-mutes, in one case a lesion of the posterior regions, in the other amyloid degeneration of the satne locality (posterior centres).* On the theory thus supported by the data furnished by 'formal and pathological anatomy, and experimental physiology, we may, therefore, legiti mately conclude that the isolated ganglions of the optic thalamus are so many independent departments for each kind of sensorial impressions, and that the destruc tion of each of them may lead to the disappearance or alteration of the function to which it is specially . devoted. t 2. The central region of grey matter which, as we have seen, lines the internal walls of the optic thalami, represents an elongation into the brain of the central grey matter of the spinal cord.
It presents the appearance of two tracts of ashen grey matter, which here and there form protuberances, which are themselves individually connected with the nerve-fibrils which are implanted in them. Such are the grey protuberances of the septum, for the internal olfactory roots ; those of the tuber cinereune, for the optic fibres the mamillary tubercles and pineal gland, for the connecting fibres emanating from the anterior centres.
It similarly receives a certain contingent of grey ascending fibres, which probably represent the centripetal spinal fibres which are distributed in these plexuses.* The central grey matter is composed of a network of anastomosing cells, forming a continuous plexus.
Since, on the other hand, we can demonstrate that the white cerebral fibres radiating from the convolutions do not all lose themselves in the small centres of the optic thalamus, but that a certain number of them, pursuing their primitive direction, are prolonged as far as the plexuses of the central grey matter, we may legitimately recognize in this anatomical arrangement the natural channel for the propagation of nervous actions emanating from the cortical periphery, and manifesting themselves in the plexuses of central grey matter ; and reciprocally, interpreting things in an inverse sense, we may recognize in this species of nerve-fibres the direct means of communication between the spheres where the phenomena of vegetative life take place, and those regions of the cortical substance which are the theatre of psycho-intellectual activity.
To sum up, the optic thalami are in a special manner the natural anatomical foci which preside over the organization and grouping of the cerebral fibres. From a physiological standpoint, the optic thalami are Inter mediary 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 soh and unique open gates by which all stimuli from without, destined to serve as. pabzdum vitae for these same cortical pass ; and the only means of communication by which the regions of psychical activity come into contact with the external world.* 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.