158 Ley ton and Sheii-in^ton 



precentral sulci, superior and inferior, also contain portions of the motor 

 cortex. These sulci are far more variable in their extent and position in 

 the anthropoid than is sulcus centralis, so that it is not easy to make a 

 ireneral statement as to the amount of motor cortex thev contain that can 

 apply strictl}^ to all cases. In the hg. 15, from a chimpanzee, is represented 

 the amount buried in them in that specimen as experimentally determined. 

 Moreov^er, the determination of the exact position of the anterior limit of 

 the motor cortex is even on the free surface a matter of some artificiality, 

 because in the anterior direction the motor field as examined by faradisa- 

 tion seems to fade oft' graduatim, so that a prolonged series of stimulations 

 in that neighbourhood produces, by inducing " facilitation," a limit set 

 farther forward than under a brief decisive examination by faradisation 

 at a restricted number of selected points. 



In his "Localisation of Cerebral Function" Campbell (8) has fur- 

 nished an admirable and full account of the structural types of cerebral 

 cortex and their topographical distribution not only in man but in the 

 chimpanzee and orang. It is instructive, therefore, to compare the limits 

 of the motor field as determined by faradisation in those anthropoids with 

 his " precentral area ' determined by cell and fibre lamination. The 

 posterior borders of the two as delimited by these two different methods 

 seem to agree so closely, that there can be little doubt that as regards that 

 limit the two fields or areas are the same. In regard to the anterior 

 border, the motor fields boundary seems to lie, especially in its lower two- 

 thirds, farther forward than does that of Campbell's precentral area. The 

 anterior boundary, as determined by faradisation, is, however, not a sharp 

 one, and its situation seems to vary somewhat from specimen to specimen. 

 As placed by us, it certainly appears to lie for the most part in the inter- 

 mediate precentral area of Campbell. Opposite the "arm area" it lies 

 not far behind the anterior boundary of the " intermediate precentral area," 

 but opposite the " leg area ' more considerably so. Opposite the " face 

 area " it lies very much farther behind the anterior limit of " inter- 

 mediate precentral area," although in front of anterior limit of the pure 

 "precentral area" of Campbell. Campbell in his original description 

 furnishes a number of arguments in favour of his " intermediate precentral 

 type ' of cortex possessing motorial functions, though differing from the 

 precentral tj^pe or motor cortex pure. The gradual shading off of the pure 

 motor field in the anterior direction, as experienced in our observations, 

 and the variability of its anterior edge, as mentioned above when faradised 

 under different experimental conditions, seem to us to lend support. to his 

 contention, although the latter is put forward on other evidence. 



On the whole, we should estimate that in the anthropoid brain the 

 portion of the motor region which lies buried in the sulcus centralis and 

 other fissures amounts to not less than about 35 per cent, of the whole 

 motor recrJon. 



