Now, it may be inferred, from their con nections with nerves chiefly of a sensitive kind, that the olivary columns, and the optic thalami, which are continuous with them, are chiefly concerned in the reception of sensitive impres sions, which rnay princitrally have reference merely to informing the mind (so to speak), or partly to the excitation of motion, as in dqIu tition, respiration, Scc. The posterior horns of the grey matter of the cord, either by their direct continuity with the olivary columns, or their union with these columns through coin missural fibres, become part and parcel of a _ .NeAVICC.
great centre of sensation, whether for mental or physical actions.
The pyramidal bodies evidently connect the grey 'natter of the cord (its anterior horns ?) with the corpora striata; and not only these, but also the intervening masses of vesicular matter, such as the locus niger, and the vesi cular matter of the pons, and of the olivary colurnns; and, supposing the corpora striata to be centres of volition in intimate connection with the convoluted surface of the brain by their numerous radiations, all these several parts are linked together for the common pur poses of volition, and constitute a great centre of voluntary actions, amenable to the influence of the will at every point.
It has been pretty generally admitted by anatomists, that both the corpora striata and the anterior pyramids are concerned in volun tary movements. The rnotor tracts of Bell were regarded by drat physiologist as passing, upwards from the anterior columns of the cord to the corpora striata, and, after traversing those bodies, as diverging into the fibrous mat ter of the hemispheres; and the fact of the origin of certain motor nerves, in connection with those fibres, was considered to be very favoumble to this view. The decussation of the pyramids, likewise, so illustrative of the cross influence of the brain in lesions sufficient to produce paralysis, has been looked upon as an additional indication of the motor influence of these parts.
The invariable occurrence of paralysis as the result of lesion, even of slight amount, in the corpora striata, must be regarded as a fact of strong import in reference to the motor func tions of these bodies.
Nor is this fact at all incompatible with the statements made by all experimenters, that simple section of the corpus striatum does not occasion either marked paralysis or convulsion; and that in cutting away the different segments of the bmin, beginning with the hemispheres, convulsions are not excited until the region of the mesocephale is involved. The influence of
the corpora striata is not upon the nerves di rectly, but upon the segments of the medulla oblongata or of the spinal cord, and, through them, upon the nerves which arise from them. Were the nerve-fibres continued up into the corpora striata, according to an opinion which has been long prevalent, there would be no good reason for supposing that they should lose in the brain that excitability to physical stimuli which they are known to possess in the spinal cord, and at their peripheral distribution.
The latest experiments of this kind, which are those of Longet and Lafargue, agree in the fol lowing result, which is not at variance with that obtained by Flourens. The animals remain immoveable after the removal of the corpom striata, whether those bodies have been removed alone or in conjunction with the hemispheres ; nor do they show any disposition to move, un less strongly excited by some external stimu lus. None of these observers had noticed the irresistible tendency to rapid propulsion, which was described by Idagendie. Itt 'nova' of the corpus striatum of one side caused weakness of the opposite side.
ln order to form a due estimate of these ex periments, it must be borne in mind, that the effects of simple excision of either corpus striatum would be very different from those of disease of it. The depressing effects of the latter would be absent, at least, until some alteration in the process of nutrition had been set up in the mutilated parts. Simple excision of the centre of volition, and inflammatory dis ease of its substance, or an apoplectic clot, must produce essentially different effects ;— the one simply cuts off the influence of the will, the other affects the vital action, and, con sequently, the vital power of the centre, and of the commissuml fibres connected with it.
Judging from structure only, it might be conjectrired that the locus niger, that remark able mass of vesicular matter which separates the anterior and posterior planes of each crus cerebri, exerts a motor influence. It resembles in structure the anterior horns of the grey matter of the cord, and contains numerous large caudate vesicles with very abundant pig ment, and is the immediate centre of implanta tion of a very important motor nerve, the third pair, which regulates the movements of nearly all the muscles of the eyeball.