ATLAS OF NERVE CELLS 



THE FOURTH LAYER, OR LAYER OF 

 POLYGONAL CELLS 



Plate L. shows the fourth or deepest 

 layer of the cortex. This layer is made 

 up of polygonal or fusiform cells, whose 

 general direction is at right angles to the 

 pyramidal cells of the third layer. One 

 such cell is shown in the plate, a fusi- 

 form cell (/), its long axis being hori- 

 zontal. It has two large protoplasmic 

 processes covered with gemmules and 

 giving off branches. It has a large 

 neuraxon which passes almost horizontally 

 toward the left, giving off collaterals, and 

 then turns downward. This cell is rather 

 larger than the majority of the cells of 

 this layer. But other cells of the layer 

 are triangular, rectangular, or polygonal (q), 

 hence the latter name has been selected 

 as descriptive of them. Cajal says that 

 a stalk is often wanting in these cells, 

 but when present it varies greatly in its 

 direction, and never turns downward or 

 upward or terminates in the superficial 

 layer of the cortex. The neuraxons of 

 these cells turn downward into the white 

 substance. 



FIG. 10. 



FIG. 10. Diagram of the cells of the cerebral cortex. The cells are repro- All anatomists have distinguished this 



duced from the plates. 



7, superficial layer, a, fusiform, />, triangular, c, polygonal cells of Cajal. 



7/, layer of small pyramids. d, smallest, e, small, / medium-sized pyramids with their neuraxons descending to the white matter, giving off 

 collaterals in their course. 



III, layer of large pyramids, g, largest (giant) pyramidal cells, k, large pyramidal cell with very numerous dendrites. All pyramidal 

 cells are seen to send long apical processes up to /. m, Martinotti cell with descending dendrites and ascending neuraxon. , polygonal cells. 



IV, deep layer. /, fusiform cell, q, polygonal cell. 



V, the white matter containing the neuraxons from pyramidal cells, d, e, f, g, and from cell of the deep layer g. r, neuroglia fibre. 



