144 Ley ton and Sherrington 



The above instances arc cited as typical and somewhat outstanding 

 examples of what in a smaller and less pronounced manner was frequently 

 met by us. As to how far such deviations, as also the reversals and facili- 

 tations, are traceable to shuutings of route in the cortical structure itself, 

 or how far they are referable to shuntings in sub-cortical paths and 

 centres, that is a question towards whose solution oui; observations contri- 

 bute little or nothing. The diagram furnished by Franz (17) (fig. Ki, 

 p. 148 in his paper) indicates the manifold possibilities in that respect, 

 and Graham Brown (3, 4) has published direct observations in regard to 

 " facilitation "' which throw light on the problem as concerns that pheno- 

 menon. The main point that we wish here to emphasise in preface to the 

 subjoined list of motor responses and maps of cortical points belonging to 

 them as observed in our experiments is, that in looking through such data 

 we would wish the reader to bear in mind that the fixity of such localisa- 

 tions is as regards minutiae to some extent probably a temporary one, i.e. 

 obtained at the time of observation, but in our opinion might not be pre- 

 cisely the same were examination possible at a number of different times 

 and in a number of different experiments. As regards minutiee of localisa- 

 tion in the motor cortex, our experience agrees with that of those (36, 5, 4, 

 17, 3) who find, as Shepherd Franz (17) expresses it, that the motor 

 cortex is a labile oroan. 



f? 



2. List of Motor Responses and the Topography of their 



Cortical Points. 



The maps (figs. 1-6, 8-9, 12-16, 19, 24, 27) which illustrate the '■ List 

 of Motor Responses " are all approximately life-size. Fig. 7 is on a some- 

 what larger scale. The maps, except figs. 7 and 13, were prepared by 

 placing a thin plate of glass upon the surface of the hemisphere and trac- 

 ing the sulci upon it. The plate Avas first applied to the brain in situ over 

 the exposed part of the hemisphere, and, where this did not afford sufficient 

 of the surrounding part of the hemisphere, the plate was reapplied after 

 removal of the brain, and the parts surrounding the originally exposed 

 portion were added to the map by tracing the sulci on the glass. To follow 

 the sulci over the convexit}^ of the hemisphere the glass was tilted succes- 

 sively in the various directions required, and those of the sulci lying in 

 contact with and slightly flattened by the plate were traced. An approxi- 

 mately true plane projection of the convex surface of the hemisphere 

 was thus obtained. On these maps the cortical points localised with their 

 motor responses listed were copied in from the maps similarly obtained by 

 the glass plate and filled in as the experiment proceeded. In the maps as 

 reproduced in illustration of this paper it has been impossible to include 

 all of the points actually observed and recorded in the experiment, because 

 the number of them written into the actual experiment-map was often 

 large, and the numerals had therefore to be written so small as to render 

 them illegible unless the size of the map were considerably enlarged in 



