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, and the same correlative arrangements exist. Indeed, while the optic thalami with their different ganglions re present the regions of passage for sensorial impressions, the grey matter of the corpora striata, with its multiple elements, represents the place of halt and reinforcement for motor stimuli radiating from the cerebral cortex.
It may therefore be said that in the brain, by virtue of the same anatomic arrangements, the regions where the phenomena of sensation occur, and those in which motor stimuli are elaborated, reciprocally maintain the same topographic relations that they have in the different portions of the spinal cord proper.
As to external configuration the mass, of the corpus striatum presents the form of a reddish grey mass, of flabby consistence*, situated in front of the optic thalamus, and, gradually diminishing from before back wards, extending as far as its posterior regions.
It follows that the mass of the corpora striata pre sents an ovoid pyriform appearance, the larger extremity directed forwards, the tapered extremity backwards, and that the optic thalamus in its antero-lateral regions is encircled with a network of grey substance having its maximum thickness anteriorly.
It follows besides, as a consequence of this anato mical arrangement, that the white converging fibres which group themselves around the optic thalamus, before arriving at their destination encounter a more or less considerable thickness of the corpus striatum, which they traverse from one side to the other, at various angles and in various directions. (Fig. 5.) The anterior convergents in particular, which run towards the corresponding regions of each optic thalamus, plunge from before backwards into the very mass of the corpus striatum, and divide it into two segments, one extra- and one infra-ventricular.* The colour of the grey matter of the corpus striatum is sensibly homogeneous, wherever it is observed. It is flabby, reddish, and composed of special anatomical elements. It is, moreover, permeated by an infinite . number of whitish serpentine filaments, which represent the terminal expansions of the antero-lateral motor fibres of the spinal cord.
In the internal and inferior regions, however, where there is a confluence of all the antero-lateral fascicles of the spinal axis which expand into the corpus striatum, we come upon a very clearly circumscribed region of firmer consistence, and yellowish colour, which is easily recognized by its peculiar striation.1 This peculiar circumscribed mass of yellowish matter, which I have more particularly designated under the name of yellow nucleus of the corpus striatum, plays an important part, as a centre of radiation for nerve fibres, in its relations with the ultimate expansions of the cerebellar peduncles.
The structure of the corpus striatum must now be considered, as regards : 1. The study of the grey matter, regarded from a his tological point of view, and as to the characters of its elements.