2. That of the nervous elements, of various crigin, which enter into relation with those proper to itself.
I. The grey matter of the corpus striatum is histo logically composed of an infinite number of large poly gonal nerve-cells with multiple prolongations, their size being in general about the same as that of the larger cells of the cerebral cortex. These cells, considered in themselves, present characters common to all the other cells. They are provided with what appear to be a nucleus and nucleolus, and present ramified prolon gations which rapidly taper away, and constitute with those of the neighbouring cells a very dense and very delicate network.
Besides these large cells just mentioned, we also meet with elements of smaller size, especially in the region of the yellow nuclei, where they are extremely abundant. Their histological characters recall in a more or less vivid manner the similar elements met with in the deep zones of the grey matter of the cerebellar con volutions. These small elements, of which the nucleus is voluminous, and of which the yellowish colour enables us to distinguish them from the surrounding corpuscles of the neuroglia, exhibit a fringe of radicles of extreme tenuity, which is lost in the network formed by the large cells. It seems, then, probable that small cells, which to some extent histologically represent the cerebellar element, enter more or less directly into co,n bination with the radiations from the large cells which represent the cerebral element.
Besides these two principal elements, we have still to describe the corpuscles of neuroglia, derived more or less directly from the sheaths of the capillaries, and a considerable number of vessels which directly penetrate from below upwards into its interior in the form of more or less rectilinear filaments. (Perforated space of Vic(' d'Azyr.) 2. The diverse elements which enter into the anatomic constitution of the corpus striatum, are divided into two special groups : 1, some may be considered as a system of fibres afferent to the corpus striatum ; 2, others as a system of efferent fibres.
i. The first group comprehends : a, on the one hand, all the cerebral fibres radiating from the different regions of the cortex, and lost in the substance of the corpus striatum (cortico-striate fibres) 0, on the other hand the ultimate expansions of the superior cerebral peduncles, which are lost in its mass, and which repre sent the specific importation of the cerebellar element into the constitution of motor phenomena.
a. (Fig. 6-6. Ir. 16.) The elements of the first group, which, on account of their origin and termination, I have proposed to call cortico-striate, belong to that mass of convergent fibres which, radiating from all points of the cortical periphery, and'' probably from the psycho-motor regions so clearly determined at the present day, take a common direction towards the central ganglions. This order of fibres, however, once arrived at the circumference of the cptic thalamus, instead of terminating like their fellows, only embrace it. Arrived at the frontier of the optic thalami and the corpora striata, these fibre: are immediately reflected from below upwards, in the form of spiroid lines, and are finally isolatedly dis tributed in the different cell-territories of the corpus striatum with which they are especially connected.
These cortico-striate fibres, which have come out of the depths of the cortical layer with the sensitive fibres, still proceed for a certain distance through the brain, in juxtaposition with these latter, as is also the case in the peripheral nervous trunks, which are composed of both sensitive and motor fibres, embraced in the same envelope. Soon, having arrived in the presence of their respective centres of attraction, they each obey their innate affinities, and are distributed, some to the centres of the optic thalamus, others to the different regions of the grey substance of the corpus striatum.
These fibres then represent, properly speaking, the natural bonds of union between the regions of the cortical substance whence proceed the different volun tary stimuli (psycho-motor centres), and the different cell-territories of the corpus striatum where they are reinforced. As regards anatomical analogies, they represent the whole group of anterior roots in its relations with the grey elements of the spinal cord.