342 MESSRS. F. GOTCH AND V. HORSLEY 



CHAPTER VII. ON BILATERALITY OF REPRESENTATION IN THE CEREBRUM, AS 

 EVIDENCED BY THE ELECTRICAL CHANGES IN THE SPINAL CORD AND 

 MIXED NERVE. 



The galvanometric method affords an excellent means of determining to what 

 extent any bilateral movements obtained in the lower limbs on exciting the cortex are 

 associated with impulses proceeding down both sides of the cord. 



It is obvious that a most important question is involved in this inquiry, that, 

 namely, of the share taken in the production of bilateral effects by the different parts 

 of the nervous system. When bilateral movements of the lower limbs are evoked by 

 excitation of one cortex, it is conceivable (a) that in the portion of cortex excited, 

 muscular movements on both sides are represented ; (b) that the excitation has 

 aroused the corresponding cortical areas in the opposite hemisphere, and thus 

 produced the bilateral effect ; (c) that the excitation has aroused the basal ganglia, 

 cerebellum, &c. ; (d) that the descending impulses, although unilateral when they 

 come into relation with the spinal centres, are then brought into relation with both 

 sides of the body. 



In order to investigate this, the first problem to solve is that referred to last under 

 (d). This, the present method, and that only is capable of doing, since by it we can 

 determine the characters of the actual descending impulses in the cord before they 

 come into relation with the bulbo-spinal centres. In this way we can ascertain to 

 what extent the impulses which descend the cord from the brain already show a 

 dual (bilateral) grouping. 



We devoted a very large number of our cortical experiments to the further elucida- 

 tion of this question, feeling that the great importance of any approach towards its 

 solution, in consideration of its bearing upon the physiological characteristics of the 

 cortical cells, was a sufficient j testification. 



It is necessary, before stating our results, to give a short categorical account of the 

 work already done in this subject, and this is the more desirable since we cannot find 

 any such resume published. 



PREVIOUS WORK ON THE SUBJECT. 



The question whether both or only the opposite of the two sides of the body are 

 represented in one cortex cerebri on the efferent or motor side has been approached 

 experimentally by relatively but few authors.* As the results hitherto obtained do 

 not by any means decide the important questions which offer themselves for solution, 



* The subject has also been considered fully from the theoretical point of view by BROADBENT 

 (' British Medical Journal,' 1876, pp. 333, 401), this author believing that bilaterality of representation 

 is always effected by commissures between the bulbo-spinal centres. 



