584 



NERVOUS SYSTEM 



Attempts have been made to subdivide the centres just indicated, 

 but most of these are hardly justified by experimental results, even in 

 monkeys. Still less can it be assumed that more restricted centres can 

 be accurately mapped 

 out in the human sub- 

 ject. It has been 

 thought proper, there- 

 fore, to describe in this 

 work those centres 

 only, the localization 

 of which admits of lit- 

 tle doubt. It is proba- 

 ble, however, judging 

 from the very recent 



Fig. 145. Diagram of a median section of the brain. 



experiments of Sher- 

 rington and Griinbaum 

 on certain anthropoid apes, that the cortical motor areas are more 

 extensive than has been supposed. The method employed by these 

 observers was to place one electrode of a feeble faradic current on 



certain parts of the ex- 



and posed cortex and the 



other on an indifferent 

 point. This was thought 

 to limit the motor areas 

 much more accurately 

 than the older method 

 with the two elec- 

 trodes applied to the 

 brain. 



In man, lesions of 

 parts of the motor-cor- 

 tical zone produce local- 

 ized paralysis, or what is 

 called monoplegia, the 

 action being crossed. 

 The following are some 

 of the more common 

 forms of monoplegia 



that have been observed to attend localized cortical lesions: I, oculo- 

 motor monoplegia (isolated ptosis); 2, facial monoplegia, sometimes 

 associated with paralysis of the hypoglossal nerve ; 3, brachial mono- 

 plegia, or paralysis of the opposite arm ; 4, crural monoplegia, or 



Fig. 146. Diagram of certain motor cortical areas. 



