1878.] 



of the Motor Area of the Brain. 



43 



those dwelt upon attach themselves to these cells, and these are of such 

 a character as to warrant us considering them apart, after having com- 

 pleted our description of the separate layers of the cortex by a brief 

 examination of the deepest stratum. 



Fifth Layer. — This series consists of fusiform or spindle-shaped cells, 

 arranged in columns by the interposition of bands of medullary fibres. 

 (Plate 1, Fifth Layer). They average in size 25/* by 9/*, the largest 

 attaining the dimensions of 32/* by 13/*. Their nuclei are almost 

 invariably oval, and measure from 11^ to 13/* in length by 6ju to 9/t. 

 in breadth. As remarked by Meynert,* these cells are not strictly 

 bi-polar, as a large proportion throw off several branches, whilst a verv 

 frequent form gives off a lateral branch from the projecting side of the 

 cell midway between either extremity (Plate 1, Fifth Layer). These 

 cells are arranged in columns as above stated, their long axis lying in 

 the plane of the intervening medullary fibres, but along the base of a 

 sulcus their long axis lies horizontally to the surface of the cortex, 

 suggesting the belief that they belong to the connecting or arcuate 

 system. An extensive series of observations was made with the object 

 of calculating the varying number of cells in the third and fifth layers 

 at different points along the ascending frontal convolution, and it was 

 found that the average number of pyramidal cells in the quarter-inch 

 field f was fifty-seven, the average number of spindle cells was forty. 

 The extremes were respectively thirty-three to ninety-nine, and twenty- 

 one to seventy-three. Although at some sites, therefore, the propor- 

 tion may increase to three times what it is at other sites, no relation- 

 ship could be traced between these variations and the alternating 

 thickness and dense groupings of cells in the remaining layers. For 

 convenience of reference we subjoin a table of measurements of the 

 cells of the different layers of the cortex in the ascending frontal 

 convolution. 





Length. 



Breadth. 



First Layer. 









6// — 9// 



6//— 9// 



Large „ 



13/.. 





11//— 23// 



6//— 9// 



Third Layer. 









12/* 



8// 





22//— 41// 



4//— 23// 



Fourth Layer. 









71// 



35,a 





126// 



55// 



Fifth Layer 



25//— 32// 



9/*— 13// 



* Op. cit., p. 389. 



f The quarter-inch field alluded to was equivalent to a circle half a millimetre in 

 diameter. 



