162 CEREBRAL LOCALIZATION 



to know whether a tumour causing hemiplegia is 

 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 assistance. 

 There is a good deal of evidence that if the paralysis 

 is of a flaccid type, the lesion is most probably 

 cortical, though the converse is not necessarily true. 

 Thiele has demonstrated in animals that tone is 

 increased by impulses from Deiter's 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 w r hich 

 subserves the 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 

 cord will probably damage the rubrospinal tract as 



* 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. 



