Activities of the Mid-Brain. 



161 



flexion of the ipsilateral arm. This area lay about 3 mm. above the tip of 

 the calamus and was near the mid-line. To stimuli of a strength which 

 could evoke this, the surrounding regions were inert. 



Stimulation of the nucleus cuneatus in the medulla oblongata gives 

 flexion of the ipsilateral arm. Stimulation of the nucleus gracilis gives 

 movements of the lower limbs. It has been found in some experiments that 

 the flexion of the arm evoked by stimulation of the ipsilateral nucleus 

 cuneatus is followed by marked flexor after-discharge. This may occur in 

 response to. very weak stimuli, and in these experiments the cerebellum had 

 been removed. The after-discharge has been found to disappear after 

 removal of all in front of the medulla oblongata, and after removal of the 

 mid-brain alone. 



IX. Conclusions. 



The " dorsal focal point " in the cross-section of the mid-brain — the 

 results of stimulation of which are here described— corresponds geographically 

 with the cross-section of the posterior longitudinal bundle at that level. 

 The " ventral focal point " (described for one experiment) corresponds 

 geographically with the area of the nucleus ruber. The effective strength of 

 stimulation of these areas is much greater than that necessary to evoke 

 reactions from the motor nuclei or from the nucleus cuneatus. 



In these circumstances there is a great risk of error due to spread of 

 current. But the fact that the reaction from the dorsal focal point is 

 abolished after lateral semi-section of the mid-brain behind the point 

 stimulated, and that the reaction may still be obtained from the caudal 

 surface of the semi-section, makes it extremely probable that the phenomena 

 here described are conditioned by stimulation of the posterior longitudinal 

 bundle. That they are apparently unchanged after mesial longitudinal 

 division of the mid-brain helps to confirm this view. Is it possible that 

 the stimulation of the " ventral focal point " is stimulation of the rubro- 

 spinal tract ? My evidence at present is quite insufficient to make this 

 certain, but there are certain points of interest which may be noted. In the 

 first place, the excitability of this point drops after mesial longitudinal 

 division of the mid-brain, and this looks as if there was a decussation of the 

 tract stimulated in the mid-brain itself. Another point which may be noted 

 is that, whereas before this mesial longitudinal division the ipsilateral reaction 

 of the ventral focal point was one of flexion, after that division it appeared 

 to yield ipsilateral extension. As I have said, the evidence on this point is 

 quite incomplete, but may the guess be hazarded that the crossed and 

 uncrossed portions of the rubro-spinal tract subserve different functions ? 



To turn again to the dorsal focal point (posterior longitudinal bundle ?), 



