THE BRAIN. 433 



written. This is called "ataxic aphasia," because it depends upon a 

 defect of nervous combination. 



Observations on the locality of the centre of language tend to place 

 it more especially in the convolutions surrounding the lower end of the 

 fissure of Sylvius, and in those of the insula. Broca refers it to the 

 posterior part of the third frontal convolution, while others consider it 

 as belonging to the frontal lobe in general. The evidence for this local- 

 ization consists in a number of instances in which aphasia has been 

 found, on post-mortem examination, to be accompanied by lesions of 

 the brain confined to the points indicated. It is often accompanied by 

 hemiplegia, but may exist independently of any paralytic affection. 



According to the majority of observers, the nervous centre for 

 articulate speech is seated upon one side of the brain only, and, as 

 a rule, in the left hemisphere. This conclusion is derived from the 

 large preponderance of cases in which aphasia is associated with 

 hemiplegia on the right side of the body rather than on the left. It 

 is still more strongly corroborated by such instances as that reported 

 by Bateman,* of chronic left hemiplegia without aphasia, followed in 

 the same individual by a sudden attack of right hemiplegia with 

 aphasia. It is not supposed that the two hemispheres are absolutely 

 different from each other in this respect; but that the functional 

 superiority of the left side, in the production of language, is like that 

 by which we are enabled to use the right hand for certain delicate 

 manipulations of which the left is incapable. A lesion of the motor 

 centres in the right hemisphere would paralyze only the ordinary 

 movements effected by the left hand ; but a lesion of the same extent 

 in the left hemisphere would further paralyze the special movements, 

 like writing or drawing, for which we depend on the right hand. It 

 is, perhaps, for a similar reason that a patient with destructive injury 

 of the left hemisphere becomes incapable of language, while one with 

 a corresponding injury on the right side is not affected in the same 

 way. This would also explain the exceptional cases in which aphasia 

 coincides with left hemiplegia ; just as certain individuals are habitually 

 left-handed, and would consequently be rendered incapable of delicate 

 manipulations by hemiplegia of the left side. 



Hemiplegia and Hemiansesthesia from Cerebral Lesions. It has 

 already been shown that hemiplegia of the opposite side of the body, 

 without alteration of sensibility, results, in man, from destructive 

 lesions of the cerebral convolutions in the motor region. It is also 

 known that hemianaBsthesia, or loss of sensibility in one lateral half 

 of the body, may take place, without paralysis of motion, from cerebral 

 disease. Both these affections may furthermore be produced by lesions 

 limited to particular parts of the white substance. This substance 

 consists of tracts connecting the cortical convolutions, through the 

 corona radiata and internal capsule, with the base of the brain, and 



* On Aphasia. London, 1870, p. 152. 

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