722 M 



PHYSIOLOGY OF ''KlE NERVOUS SYSTEM. 



great centre of sensation, whether for mental or 

 physical actions. 



The pyramidal bodies evidently connect the 

 grey matter 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 

 columns ; 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. 



Tt has been pretty generally admitted by 

 anatomists, that both the corpora striata and 

 the anterior pyramids are concerned in volun- 

 tary movements. The motor tracts of Bell 

 were regarded by that 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 

 favourable 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 brain, 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 corpora 

 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 Magendie. Removal of the 



corpus striatum of one side caused weakness 

 of the opposite side. 



In 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 commissural fibres connected with it. 



Judging from structure only, it might be 

 conjectured that the locus niger, that remark- 

 able mass of vesicular matter which separates 

 the anterior and posterior planes of eacli 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 tlie muscles of the eyeball. 



Optic tliahnni. The same line of argument 

 whicli leads us to view the corpora striata as 

 the more essential parts of the nervous appa- 

 ratus which controul direct voluntary move- 

 ments, suggests that the optic thalami may be 

 viewed as the principal foci of sensibility, 

 without which the mind could not perceive the 

 physical change resulting from a sensitive im- 

 pression. 



The principal anatomical fact which favours 

 this conclusion is the connection of all the 

 nerves of pure sense, more or less directly, 

 with the optic thalami or with the olivary co- 

 lumns. The olfactory processes, which appa- 

 rently have no connection with them, form, no 

 doubt, through the fornix, such an union with 

 them, as readily to bring them within the in- 

 fluence of the olfactory nerves. 



According to this sense of its office we must 

 regard the optic thalami as the upper and chief 

 portions of an extended centre, of which the 

 lower part is formed by the olivary columns, 

 which we have already referred to as taking 

 part in the mechanism of sensation. The con- 

 tinuity of the olivary columns with the optic 

 thalami justifies this view : nor is it invalidated 

 by the fact, that some of the nerves which 

 arise from the medulla oblongata are motor in 

 function; for Selling's researches render it 

 probable that these fibres have their origin in 

 special accumulations of vesicular matter, which 

 contain caudate vesicles of the same kind as 

 those found in the anterior horns of the grey 

 matter of the cord. 



The results which experiments have yielded 

 add little that is positive to our knowledge of 

 the functions of these bodies. Flourens found 

 that neither pricking nor cutting away the optic 

 thalami by successive slices occasioned any 

 muscular agitation, nor did it even induce con- 



