1878.] 



of the Motor Area of the Brain. 



45 



The breadth of these cells was again tested by their measurement in 

 several sections cut at right angles to their long diameter. In this case 

 156 cells averaged 35//-. The nucleus averaged 13/t long, by 9/t 

 broad, the extreme length 20 ju, extreme breadth 12 juu. 



3rd. Processes. The average number of secondary processes* arising 

 from ninety of these cells was seven, the largest number observed was 

 fifteen. Sections across the long axis of the cell, however, occasionally 

 brought into view as many as eighteen, and exhibited the cell as 

 occupying the centre of an extensive area over which its branches 

 spread, radiating outwards and downwards from all points of its 

 margin. From this mode of branching it will, of course, be apparent 

 that the absolute number of processes given off by a single cell 

 cannot be determined with any degree of certainty, and that state- 

 ments with regard to the comparative number of such in man and 

 the lower animals must be received with extreme caution, as the 

 number exhibited will vary with the direction of the section and the 

 methods employed for examination. It will be readily conceived how 

 the fresh method of preparation described by one of the authors of 

 this paper,f brings into view a far larger number of processes than 

 are observed by other methods of preparation. 



4th. Distribution. The facilities afforded by the ether-freezing micro- 

 tome, % have enabled the writers to examine in rapid succession and 

 under most favourable conditions extensive portions of the same brain 

 in a perfectly fresh state, and with but little trouble a series of convo- 

 lutions may thus be sliced from end to end and the sections examined 

 seriatim. The results of such an examination have been to demon- 

 strate the very important fact that these " giant, cells " are distributed 

 over certain definite areas which are remarkably constant, and it- 

 appears to the authors that these cell-groupings are especially and 

 exclusively a characteristic feature of the motor area, as defined by 

 Ferrier. That these giant cells may be found in isolated positions at parts 

 not included in the motor area the writers do not question ; but they 

 have not succeeded in finding any large groups or distinct areas of such 

 elements in portions of the cortex at a distance from this region of the 

 motor centres. The present investigation has been limited to a portion 

 of the motor area, viz., the ascending frontal and two upper frontal 

 convolutions ; but it is hoped that this attempt to sketch the topogra- 

 phical distribution of these cells may prove but the introduction to a 

 more complete and accurate investigation of the histology of individual 

 convolutions. Such an investigation must eventually be made if 

 scientific precision is aimed at by the histologist in the field of cerebral 



* By secondary processes we mean all branches, exclusive of the two main 

 branches — the basal and apical. 



f Monthly Microscopical Journal, Sept., 1876. 



X Vide Journal of Anat. and Phys.. April, 1877, and Mo. Micros. Journal. 



