1886.] ON THE CORTICAL CENTRES OF TIIE MONKEY. 475 



II. "A Minute Analysis (experimental) of the various Move- 

 ments produced by stimulating in the Monkey different 

 Regions of the Cortical Centre for the Upper Limb, as 

 denned by Professor Ferrier." By Charles E. Beevor, 

 M.D., M.R.C.P., and Professor Victor Horsley, F.R.S., 

 B.S., F.R.C.S. Received June 4, 1886. 



(Abstract.) 



The following investigation was undertaken as prefatory to a 

 research into motor localisation of the spinal cord. 



Anatomy. — (1.) Attention is drawn to soma minute details of the 

 topographical anatomy of the upper limb centres as defined by 

 Professor Ferrier. 



(2.) Outlines of the shape and arrangement of the fissure of 

 Rolando, the precentral and intraparietal sulci. 



(3.) Proof adduced in support of the authors' opinion that the 

 small horizontal sulcus named X by Professor Schafer really corre- 

 sponds to the superior frontal sulcus of man. 



Previous Besearches. — Ferrier's results are then given in full. 



Method of Experimentation is explained in detail, as also the mode of 

 subdivision of the part of the cortex investigated into centres of 

 about 2 mm. square. 



From the results of excitation are then deduced the two following 

 axioms : — 



Axiom I. — Viewing as a whole the motor area of the cerebral cortex 

 for the upper limb, as defined by Professor Ferrier, we find that the 

 regions for the action of the larger joints are situated at the upper 

 part of the area, i.e., closer to the middle line, while those for the 

 smaller and more differentiated movements lie peripherally at the 

 lower part of the area. 



Axiom II. — As a broad result, extension of all the joints is the most 

 characteristic movement of the upper part of Ferrier's arm centre ; 

 while flexion is equally characteristic of the movements obtained by 

 stimulating the lower part. Finally, between these two regions there 

 is a small portion where flexion and extension alternately predominate, 

 a condition to which we have given the name of confusion. (Here 

 both flexors and extensors are contracting at the same time, and 

 consequently the joint is usually fixed in a neutral position, each 

 group of muscles alternately drawing it in opposite directions.) 



In confirmation of the facts supporting these axioms, reference is 

 made to a table, the details of which are expanded. 



Priority of Movements is found to take place in the order given in 



