34 Precentral or Motor Area [CHAP. 



of the Rolandic fissure correspond to the cortical distribution of the facial nerve. If this 

 localisation of the cortical representation of movement be correct, it will go far to explain 

 the significance of the variations in size of these " motor " cells, and especially will it strengthen 

 the thesis expressed in Bevan Lewis' words that " the greater the distance along which a 

 nerve cell has to transmit its energy the larger will that nerve cell probably be " ; for the largest 

 cells are exactly those whose impulses have to travel down to the muscles of the lower 

 extremity, those for the arm being quite a third smaller ; and while the cells for the control 

 of trunk muscles are so small that doubt is necessarily thrown on the thesis, it must be 

 pointed out that the whole mechanism affecting these muscles is not so highly specialised as 

 that of the extremities ; also that the intermediaries in the neuronic chains which govern 

 the trunk, viz. the anterior cornual cells in the dorsal region, are very insignificant compared 

 with analogous cells in the cervical and lumbar enlargements; and furthermore, that the muscles 

 in which the issuing nerve terminates are but slightly removed from their point of origin. 

 That the cells in the face region should be small is also not surprising. 



Before dismissing this question I must mention that Dr Hughlings Jackson has promulgated 

 the belief that the magnitude of the cell varies in proportion to the size of the muscle it 

 controls, or as he prefers to call it, ' the size of the movement " ; thus, the " small movements " 

 of the hand require small cells and the " large movements " of the shoulder large cells. But 

 in my belief this ingeniously conceived principle, tenable in all other respects, fails in one 

 important particular, it fails as regards trunk representation ; for I take it that the movements 

 in which the trunk muscles engage are essentially " large movements," and therefore the trunk 

 area should harbour large cells ; if, however, my localisation of that area be correct, this is not 

 the case. 



Other factors supposed to have some influence on the size of the nerve cell and considered 

 by Bevan Lewis are the age of the cell and the complexity of its surrounding connections, but 

 in my opinion these have little physiological importance. Likewise, some observations of Betz's 

 to the effect that these cells are larger and more numerous in the right hemisphere than in 

 the left, and also that their number is lacking in young individuals, are open to grave doubt. 



The Number of Giant Cells in the Precentral Region. (Plate IX.) 



Although, at first thought it might seem foolish to attempt an enumeration of the giant 

 cells present in the human motor area, yet on account of the prominent manner in which 

 they stand out in sections specially prepared for their display, this is really not so difficult of 

 accomplishment ; and in the case of one hemisphere, of which the central convolutions were 

 cut strictly seriatim in celloidin, I stained and counted the cells in every fifth section which 

 came off the microtome and the resulting estimate of the total number of giant cells I put 

 down as approximately 23,000. Of course it must be admitted that such a calculation can only 

 be roughly accurate, but in compiling it I endeavoured to avoid error as much as possible by 

 including in the count only those cells which showed a nucleus and nucleolus. 



To illustrate the numerical display of these cells at different levels in the precentral 

 gyrus, I cannot do better than give a table showing the numbers of cells counted in a series 

 of sections cut at right angles to the fissure of Rolando and taken at intervals of 5 mm. all 

 the way along its course. 



