226 CEREBRAL LOCALIZATION 



accessible, either in the cortex or close beneath it, 

 or inaccessible, in the internal capsule or isthmus. 

 The principal evidences of the former are the occur- 

 rence of monoplegias, the face, arm, or leg being 

 affected alone without the others, whereas lesions of 

 the internal capsule would paralyse all three ;* 

 secondly, persistent aphasia may be present ; and 

 thirdly, there may be recurring convulsions. The 

 degree of sensory impairment is not of much assist- 

 ance, but the considerations just advanced may 

 sometimes.be helpful. 



There is a good deal of evidence that if the paral57sis 

 is of a flaccid typ^ the lesion is most probably 

 cortical, though ^'.le converse is not necessarily true. 

 Thiele has demonstrated in animals that tone is 

 increased by impulses from Deiters' nucleus in the 

 medulla, and inhibited by impulses generated in the 

 optic thalamus and conducted by the rubrospinal 

 tract (Monakow's bundle). It is this tract which 

 subserves thfr stock movements such as standing and 

 walking, which can often be carried out after complete 

 destruction of the pyramidal tract. In man, a 

 cortical lesion is often (not always) accompanied by 

 a flaccid paralysis with no Babinski sign and with 

 normal or diminished reflexes (see cases quoted by 

 Bergmark) , but when the optic thalamus and internal 

 capsule are involved, there is always marked rigidity. 

 Pressure on the isthmus, pons, medulla, or spinal 



* In monkeys the fibres to the head, arm, and leg are grouped 

 in bundles in the internal capsule, but apparently this is not the 

 case in man, and consequently small lesions cause mild hemiplegia, 

 not monoplegia. 



