492 THE BRAIN. 



animals, and yet the power of motion and of sensibility may be retained 

 to a considerable extent. 



It is certain, however, from the known facts of pathology, that their 

 influence is an important one, since, in man, lesions of these ganglia are 

 almost always followed by more or less complete hemiplegia on the 

 opposite side of the body. In general terms, the effect of cerebral 

 hemorrhage, whether from injury or disease, may be said to vary accord- 

 ing to its location; hemorrhage upon the surface of the hemispheres 

 producing coma, that in the cerebral ganglia causing hemiplegia. The 

 usual significance attached to the term " hemiplegia" is that of loss of 

 voluntary motion on one side, while a corresponding loss of sensibility 

 is designated as hemiansesfhesia. In cases of lesion of the cerebral 

 ganglia or adjacent parts, the loss of motion is usually the most promi- 

 nent symptom, hemiansesthesia being either entirely absent or disap- 

 pearing rapidly, while the motor paralysis lasts a longer time. On the 

 other hand, hemiansesthesia may continue after the power of motion is 

 recovered, and it may also be produced in animals by lesions of the 

 brain without being accompanied by any muscular paralysis. 



Attempts have been repeatedly made by various authors to locate 

 more distinctly the physiological acts of sensation or motion in one or 

 the other of the cerebral ganglia separately ; but thus far these attempts 

 have not been so successful as to command general assent. The most 

 exact experiments in regard to sensibility are those of Yeyssiere, 1 who 

 operated by introducing into the brain of the dog a slender trocar 

 armed with a spring, which could be expanded at the bottom of the 

 wound and thus produce, by rotation of the instrument, a lesion of 

 the deeper parts of the brain without serious injury of the more super- 

 ficial portions. After study of the symptoms caused by the operation, 

 the animal was killed, and the exact location of the injury ascertained. 

 The observer found by this means that hemiansesthesia, either alone or 

 accompanied by more or less paralysis of motion, was produced by 

 lesions of the cerebral ganglia and the white substance included be- 

 tween them ; but that it was the white substance of the internal capsule 

 which was most constantly affected in these cases. The gray substance 

 of the cerebral convolutions, as well as that of the cerebral ganglia, 

 might be extensively injured without causing loss of sensibility; but 

 this effect was produced in proportion to the extension of the injury 

 to the internal capsule and the commencement of the expansion of 

 radiating fibres derived from it. 



The above experiments and observations do not show that the physio- 

 logical functions, either of sensibility or voluntary motion, are seated 

 in the cerebral ganglia or the internal capsule. The paralysis of motion 

 and sensation resulting from injury to these parts is due evidently, in 

 great measure, to the shock communicated, through descending fibres, 

 to other parts of the brain below ; since, as in several of Yeyssiere's 



1 Recherches sur riTemiansesth^sie de cause cr6brale. Paris, 1874. 



