THE CEREBRUM, AND ITS FUNCTIONS. 743 



which are far better explained on the idea that these radiating fibres are of a 

 commissural nature only, serving to connect the vesicular matter of the Cerebrum 

 with that of the higher portions of the Cranio-Spinal Axis, through which alone 

 they are brought into relation with the central terminations of the afferent 

 nerves, and with the origins of the motor. On this view, the Cerebrum would 

 receive all its sensory impressions by the commissural fibres that connect it with 

 the ganglia, which are the real centres of these nerves ; whilst it would call the 

 motor trunks into action, by exciting, through another set of commissural fibres, 

 the vesicular matter of the ganglionic centres from which they pass forth. The 

 idea that there is no direct continuity between the radiating fibres of the Cere- 

 brum and the fibres of the nerve-trunks derives support from the fact, in which 

 the results of all experiments agree, that no irritation of the former produces 

 either sensation or motion. These results are borne out by pathological ob- 

 servations in Man ; for it has been frequently remarked, when it has been 

 necessary to separate protruded portions of the Brain from the remainder, that 

 this has given rise to no sensation, even in cases in which the mind has been 

 perfectly clear at the time, nor has any convulsive action been produced. Such 

 evidence, however, is by no means conclusive on the point ; since the same is 

 true of the Thalami Optici and Corpora Striata, in which there is more decided 

 evidence of the absolute continuity of fibres from the nerve-roots to the vesicular 

 substance of these parts respectively. 



776. The Commissural fibres constitute two principal groups, the transverse, 

 and the longitudinal; the former connecting the two Hemispheres with each 



[Fig. 194f. 



This figure is intended to show the course and connection of the fibres of the great transverse commissure of 

 the hemispheres or corpus callosum. The dissection has only been carried into the right hemisphere. It will be 

 seen that these fibres ascend to the convolutions above the mesial line, p p P. Fibres of the corpus callosum 

 radiating into the hemispherical ganglion. B. Left hemispherical ganglion undissected. E. Cerebellum. 

 Near the centre of the drawing, and a little to the right of the mesial line, is the representation of a broken 

 fasciculus of fibres the part torn off was traced most carefully into the convoluted surface of the brain. ED.] 



