ON THE MAMMALIAN NERVOUS SYSTEM. 



351 



other, it is clear that the association through the superior peduncle of the cerebellum 

 affords a means whereby the opposite lobe of that organ might be aroused, and so 

 produce the tonic contractions of the limb on the side of excitation. This view is 

 suggested to us more especially by the teachings of Dr. HUGHLINGS JACKSON, and it 

 obviously must be excluded before a positive opinion can be expressed as to the 

 bilateral representation of the limbs in the excitable cortex of one hemisphere. 



From none of the foregoing researches can it be determined to what extent the 

 bulbo-spinal centres are associated with bilateral movements, since in all experiments 

 in which muscular contractions are taken as an index their functional activity is 

 included. 



Having laid before the reader these general considerations by way of preface, we 

 will proceed to describe our own experiments, as far as they suggest fresh evidence for 

 or against the different views just enunciated. 



EXPERIMENTAL RESULTS IN CONNECTION WITH BILATEKALITY. 



The obvious elimination which the use of our method enables the experimenter to 

 obtain is the removal of the influence of the bulbo-spinal centres. 



This elimination is effected by the division of the spinal cord in the dorsal region, 

 and the observation of the electrical changes occurring in its central end when the 

 lower limb area of the cortex cerebri is excited. It is, however, essential to divide the 

 descending tracts in the cord into two halves. This is done by splitting the cord 

 longitudinally in its antero -posterior plane. The mode of operation employed has been 

 described in Chapter III., Section 2,* and the preparation shown in Plates 31 and 33. 



* It might reasonably be conceived that this operative procedure would seriously impair the con- 

 ducting power of the cord. Although, as we point out in Chapter III., the posterior columns suffer some- 

 what, this is not the case with the lateral columns, the seat of the pyramidal tract to be investigated. 

 An example of this is to bo seen in the following case, where the effects in the divided cord of exciting 

 but one hemisphere do not, when summed, fall far short of the effects obtained before the longitudinal 

 section : 



