in] 



SUMMARY. 



1. Making use of various members of the anthropoid ape family as material for experiment, 

 Professors Sherrington and (iriinbnum in collaboration have arrived at the conclusion, that 

 the motor area is, roughly speaking, limited to the precentral convolution, and in this chapter 

 a quantity of histologies,! evidence is advanced to show that the same localisation probably 

 obtains in the case of the human being. 



2. Examining the arrangement of nerve fibres and the types of cell-lamination in the 

 brains of some of the animals which Professors Sherrington and Griinbaum had previously 

 operated upon, I found that it was possible to map out a histological area which agreed very 

 closely with that which responded to electrical excitation. 



3. Extending my observations to the human brain I have discovered that a similar 

 arrangement and disposition of elements obtain therein. 



4. The cortex of the excitable area in the anthropoid ape, and of what I take to be 

 the analogous area in the human being, are distinguished by a wealth of nerve fibres, 

 noticeable in all layers or systems, which is infinitely greater than that possessed by any 

 other part of the brain surface. 



5. The area exhibiting this type of fibre arrangement is practically confined to the 

 precentral gyrus and to a portion of the paracentral lobule, and it is important to notice 

 that the floor of the fissure of Rolando forms a very definite and constant posterior limit. 



6. The same area corresponds approximately with the distribution of the giant or "motor" 

 cells of Betz and Bevan Lewis, the chief difference being that it is somewhat more extensive. 



7. I have been able to confirm Bevan Lewis's observations concerning the variations in 

 arrangement, numerical representation and size exhibited by the giant cells at different levels, 

 but I cannot agree that the cells found in the hinder part of the paracentral lobule, and 

 in the upper sixth of the postcentral gyrus, pertain to the " motor " cell category. 



8. I have found that the area described by Bevan Lewis and Henry Clarke as being 

 ban-en of "motor" cells corresponds in position with the structure known as the superior 

 deep annectant gyrus of the fissure of Rolando, and I have come to the conclusion that a 

 great deal of importance is to be attached to this structure. It marks the point of union 

 of the two original foetal subdivisions of the fissure; it is invariably present and, more 

 frequently than is supposed, rises to the surface and interrupts the fissure; the superior genu 

 is merely its expression on the surface ; it is present in the anthropoid brain, but is more 

 variable in position ;' and physiologically it seems to be an important guide to the point 

 where the trunk area intervenes between the leg and arm areas. 



9. Strong confirmatory evidence in support of the assumption that, in man as well as 

 in the man-like ape. the elements controlling volitional muscular movements are confined to 

 the precentral gvrus and its paracentral annex, is afforded by an examination of the brain 

 in cases of Amyotrophic Lateral Sclerosis, a disease limited in its affection to the muscular 

 system and to the motor system of neurones. From cursory examinations of the cortex by 

 previous observers we have learned that the " motor " cells are liable to destruction in this 



