THE CEREBRAL CORTEX 69 



fine straight fibres, with bead-like swellings at regular intervals, are to be seen extending through 

 the layer. These are thought by Retzius to be neuroglia fibres. 



Plate XL 1 1 1. shows another group of pyramidal cells (g) with the same characteristics as 

 those in Plate XLII. In this plate the axis cylinder process or neuraxon of several of the 

 cells is well shown. It can be seen to issue from the base of the cell, and to pass 

 downward toward the white matter in a wavy course, and to give off little collaterals here 

 and there, some of which appear to turn backward, as if to ascend. Cajal affirms that some 

 collaterals do turn upward and pass into the superficial layer to ramify among the horizontal 

 fibres. In this plate, also, a varicose neuroglia fibre is to be traced. It will be noticed that 

 in the layer beneath the pyramids, where no cells are stained, there are many more fibres 

 of horizontal direction than in the second layer. 



Plate XL IV. shows the characteristics of the pyramidal cells already described. The 

 neuraxon of the cell in the centre of the plate is well shown, and the very great difference 

 in its appearance from that of the dendrites is to be noticed. A small collateral is seen to 

 come off from this neuraxon near to the lower limit of the plate. 



Plate XLV. shows another pyramidal cell of medium size from the third layer (k). It 

 is given in order to ' demonstrate the branches which often come off from the apical process 

 and ascend at its side. It also shows the divisions and subdivisions of the dendrites given 

 off from the body of the cell, and the tendency to varicose swellings along these dendrites, 

 particularly at the point at which a branch is given off. 



In Plate XLVI. a single pyramidal cell is shown with its axis cylinder or neuraxon 

 under a very high power of magnification. This is seen to run from the base and to divide 

 into two branches; each branch then divides, and from these branches smaller collaterals are 

 given off. This cell is one of the cells of Golgi's second type, in which the axis cylinder 

 has no long course or definite destination, but loses itself in a plexus of very fine nerve 

 fibres. It was impossible to focus both cell and fibre upon the plate at once, with this very 

 high power, hence the cell is not clearly shown. 



