64 Precentral or Motor Area [CHAP. 



disease. This evidence I can now supplement, by stating that in two cases which I have 

 examined exhaustively, I have observed a wholesale disappearance of these elements throughout 

 their normal area of occupation, and while there was a coexistent disturbance of other elements 

 in the precentral cortex the postcentral gyrus entirely escaped affection. 



10. Valuable material for the determination of differential localisation in the motor 

 field is provided by the brains of individuals who have been disabled by amputation of one 

 or other extremity, for in due course, either as a result of section of the fibres with which 

 they stand connected, or of suppression of the energy which they elaborate, the cortical 

 "motor" cells controlling muscles in the amputated member undergo the change described 

 by Marinesco under the name " reaction a distance," and from a careful examination of the 

 distribution of these changes important results are forthcoming. 



In two cases of amputation of the leg a short distance below the knee, I have found 

 changes limited to the upper extremity of the precentral gyrus and its paracentral annex, 

 in other words to the part which in the case of the higher ape seems to control movements 

 of the toes and ankle. In another case of amputation at the knee joint, associated with 

 great atrophy of the thigh muscles, the changes extended further outwards, but numerous 

 cells above the superior annectant gyrus remained intact ; the latter probably govern hip 

 movements. In two cases of amputation of the arm through the humerus, degenerated cells 

 were found over an extended area corresponding very closely with Professors Sherrington and 

 Grunbaurn's experimentally located areas for finger, wrist, and elbow movements; and in one 

 of these cases, which was associated with extreme wasting of the shoulder muscles, a large 

 group of cells lying immediately below the superior annectant gyrus, was affected. In a case 

 of amputation of the hand the changes were limited to the lowermost part of the last- 

 mentioned area. 



11. It is impossible to reconcile these findings with the long list of clinical observations, 

 adduced in the past to support the view that the two central convolutions have an equal 

 share in the control of volitional movements, and it is suggested that natural lesions such 

 as cerebral softening, cerebral tumour, and cerebral trauma, which form the basis of most 

 of those observations, are only in rare instances sufficiently limited in their effects to allow 

 of safe judgment on this question, hence errors have arisen. 



12. The conclusions deduced from clinical observations, from experimentation and from 

 histological investigation, are completely in agreement concerning the sequence of representation 

 of movement along the course of the motor area. 



13. The giant cells disappear before the lower extremity of the fissure of Rolando is reached, 

 and are consequently not found over that cortex which we regard as the face area ; in this 

 area, however, large cells are found differing from the large pyramidal cells common to the 

 whole precentral area and these are possibly special presiding elements. 



14. It is probable that the fibres of the postcentral gyrus acquire their medullated 

 sheath before those of the precentral, but a final statement on this point is required from 

 those who have made a special study of the developing brain. 



