CHAP, vi.] THE BRAIN. 637 



make their way to or from the peripheral organs and the cerebral 

 convolutions. The injury to the basal ganglia blocks the way. In 

 the great majority of cases, the anaesthesia (or loss of sensation) 

 and akinesia (or loss of movement) are absolutely confined to the 

 opposite side of the body ; and the cases in which a lesion of the 

 basal ganglia of one side of the brain affects the same side of the 

 body or both sides, must be regarded as exceptional, and explicable 

 as the results of the action of one side of the brain on the other 

 side either of the brain or of some region of the cerebro-spinal axis. 

 The results of experiments on animals agree entirely with the 

 general experience of pathologists, that lesions of the corpora 

 striata and optic thalami produce their effect on the opposite side 

 of the body. Whatever be the view taken concerning the de- 

 cussations of sensory and motor impulses in the spinal cord (see 

 p. 601), it must be admitted that both kinds of impulses cross 

 over completely somewhere during their transmission to and from 

 the basal ganglia and the peripheral organs. 



When however we have admitted that these bodies act, as it 

 were, the part of middlemen between the cerebral convolutions 

 and the rest of the brain, we have gone almost as far as facts will 

 support us. We are not at present in a position to state dogmati- 

 cally what is the nature of the mediation which either body 

 respectively effects. A very tempting hypothesis is one which 

 suggests that the corpora striata are concerned in the downward 

 transmission and elaboration of efferent volitional impulses, and 

 the optic thalami in a similar upward transmission and elaboration 

 of afferent sensory impulses ; and there are many facts which may 

 be urged in favour of this view. 



The evidence in this matter afforded by pathology is perhaps the 

 most consistent, but not wholly so. A number of cases may be cited 

 to shew not only that lesions of a corpus striatum may be accom- 

 panied by akinesia without anaesthesia, but that lesions of an optic 

 thalamus may cause anaesthesia without actual akinesia, that is 

 without any further interference with the execution of voluntary 

 movements than is occasioned by the loss of the coordinating 

 sensations. Of these two classes of cases, the latter is the more 

 valuable, since all clinical experience shews that any lesion more 

 readily interferes with volitional movements than with the reception 

 of sensory impressions. Convulsions are not common when the lesions 

 are confined to these bodies; but when witnessed they can generally 

 be referred to the corpora striata rather than to the optic thalami ; 

 like the paralysis, the convulsions are generally limited to the 

 opposite side of the body, though feeble movements may occasion- 

 ally be seen on the same side as well. But it would be dangerous 

 to trust too much to evidence of this kind; for numerous cases 

 have been recorded where an injury apparently confined to one 

 corpus striatum has had as part of its results anaesthesia of the 

 opposite side of the body; and others where disease apparently 



