36 Precentral or Motor Area [CHAP. 



and number of fibres in the zonal layer above these cells, and of an extension of the fibre 

 wealth beyond the limits of the cell deposit, accords with a physiological fact one which I 

 do not think I have mentioned hitherto that the excitory field exceeds the Betz cell area. 



In reference to the limits of the Betz cell area on the mesial surface of the hemisphere, 

 and the question of the spread of Betz cells over the contiguous part of the ascending parietal 

 convolution, I think Betz is responsible for the statement, that the distribution of the cells 

 here is not influenced by the upper extremity of the fissure of Rolando, more, that such cells are 

 to be found in the upper sixth of the ascending parietal convolution ; but in my opinion, Betz, 

 and others who have followed his lead on this point, are in error. It is not to be denied 

 that remarkably large cells are present in the cortex coating this part, but when we arrive 

 at a consideration of the " postcentral " cortex, I shall point out striking differences between 

 these and Betz cells, I shall also show that a coexistent stellate layer can be clearly defined, 

 and that the fibre arrangement is of a "postcentral" and not of a "precentral" type; and while 

 admitting that at the exact line where the "precentral" and "postcentral types" of cortex join, 

 there is a confusion of cortical elements, I think it correct to say that Betz cells are not to 

 be found in tin- hindmost part of the paracentral lobule, that is, the part lying posterior to 

 the upper extremity of the fissure of Rolando, and coterminous with the postcentral gyms. 



Since the annectant Rolandic gyms or buttress is relatively barren as regards Betz cells, 

 it might be supposed that its fibre endowment would be on a similar poor scale, but in 

 point of fact the interruption in fibre wealth, if existent, is not at all obvious. 



The floor of the fissure of Rolando is again a posterior limit, and Betz cells can generally 

 be traced down the length of the fissure to within about 10 mm. of the inferior extremity. 



The anterior limit is not definitely related to any of the frontal fissures, and, in the lower 

 third of the area, the genuine Betz cells are almost entirely concealed in the Rolandic wall '. 



Cell Lamination of the Precentral Cortex in the Anthropoid Ape. 



My remarks under this heading are founded on a full examination of the central con- 

 volutions of one chimpanzee, and, in taking my observations I employed thionin-stained duplicates 

 of serial sections of a brain which had been previously made use of in investigating the cortical 

 nerve fibre arrangement. The employment of such duplicate sections proved doubly advantageous, 

 for not only was I able to study the cell characters, but an easy and accurate comparison 

 between the topographic distribution of "motor" fibre formation and "motor" cells was rendered 

 possible. 



Disregarding minor differences and confining my remarks exclusively to the large "motor" 

 cells, I find, in the first place, that in the ape's cortex these elements stand out with even 

 greater prominence than they do in that of the human being, a fact which I unhesitatingly 

 ascribe to the comparative smallness and paucity in chromophilic constituents of the surrounding 

 " large " pyramidal cells ; for this reason, their number and distribution can be determined with 

 great ease. I might also mention, in regard to configuration, that the typical anthropoid giant 

 cell is more elongated and has more the appearance of an attenuated pear, than the human 



1 Since writing the above I have received a paper published recently by Karl Brodmann and dealing with the Betz cells. 

 Working in Professor Vogt's laboratory in Berlin, he has examined the central convolutions seriatim in Nissl specimens, 

 and although he does not enter into topical variations, he gives the cells a distribution agreeing exactly with that 

 described above. 



