32 Precentral or Motor Area [CHAP. 



variations. (The position of these cell groups is roughly indicated by the black circles in 

 text figure 4.) Bevan Lewis and Clarke further pointed out that these cells, be they large 

 or small, lose their nest-like arrangement towards every sulcus, and at the base of the sulcus 

 always form up in an extended single file, spoken of as the solitary type of arrangement. 



Although I have acquired considerable familiarity with these elements from a study of 

 the same in cases of Amyotrophic Lateral Sclerosis and Amputation, as well as from a serial 

 examination of the central convolutions from three additional cases, which I have deemed it 

 necessary to make as a control to the results obtained from this pathological material, and 

 which I have carried out over and above my routine examination of the entire cerebral 

 surface, I wish to add nothing to the above-mentioned description of the arrangement of 

 these cells. 



Supplementary remarks are, however, justifiable concerning the significance of the topical 

 variations in cell magnitude, number, arrangement, and distribution, which occur along this 

 stretch of cortex, and a question which I am particularly anxious to explain is whether all 

 or any of these variations can be pointed to as the histological expression of an alteration in 

 function, whether, in other words, the different points, where the areas for the control of the 

 arm, trunk, leg, etc., meet, are marked by a corresponding change in histological structure, 

 and it is to an elucidation of this subject that my examination has been particularly directed. 



In discussing the question I shall first offer a few remarks on the cell-lamination of the 

 upper precentral buttress. Finding that the cells in this formation could not be studied 

 satisfactorily in transverse sections, as the cortex on the sides of the projection was always 

 cut obliquely and its structure thereby obscured, I removed the precentral gyrus from one 

 hemisphere and examined the Rolandic surface in a series of sections running in a vertical 

 instead of the usual transverse direction. Instructive in other ways, these gave an excellent 

 view of the cell-lamination of the buttress in question, and on the previously-observed rela- 

 tive barrenness of this part as regards giant cells one now obtained proof which was wholly 

 convincing. For in proceeding from above downwards it was noticed that the moment the 

 upper margin of the buttress was reached, the nests of Betz cells, which had been previously 

 rich and numerous, abruptly ceased. While in crossing the buttress it was observed not only 

 that there was a complete absence of nests of large cells, but, also, the solitary individuals 

 present were separated from one another by a distance of 2 to 3 mm. Scattered over the 

 buttress, however, numerous cells were seen, which in regard to configuration and staining 

 reaction certainly resembled Betz cells, but which one hesitated to include in that category 

 on account of their infinitely smaller size. Below the buttress the cluster arrangement 

 recommenced, although the appearances presented by the cortex above were, as I shall mention 

 presently, not altogether repeated. 



Histologically, therefore, this annectant can be proved to be an important interrupting 

 barrier, and reference to Bevan Lewis and Henry Clarke's articles on the topographical distribution 

 of the Betz cells discloses the interesting fact that the barren area they describe virtually agrees 

 in position with this buttress. 



In discussing the topographic distribution of function in the motor area, I shall have 

 occasion to mention that this buttress probably constitutes one important line of demarcation 

 between physiological subdivisions. 



