MICROSCOPIC JA.r/'o.J/r OF THE ORGANS. 



mainly to nerve fibres lying parallel to the surface, the so-called 

 tangential fibres. In this layer we find the cells of Cajal, which 

 are spindle-shaped, pyramidal, or stellate cells, whose processes 

 run horizontally in every direction, giving off fibres to the sur- 

 face of the cortex. These are considered generally as nerve eel Is. 

 Small Pyramidal Cell Layer. This zone owes its name 

 to the fact that it is made u*p of comparatively small cells of a 

 pyramidal form, so arranged that the apices are directed toward 

 the surface of the cortex, and the bases in the opposite direction. 

 Fig. 69 represents such a cell and illustrates the relation of 

 the axone and dendrites to the cell body. From the apex of the 

 cell the main dendrite proceeds toward the surface of the 

 cortex, passing through almost the entire thickness of the 

 molecular layer. Throughout its course it gives off numerous 

 side branches, and ends freely after many arborizations in the 

 outer part of the molecular layer. Other smaller dendrites 

 proceed from the lateral and basal parts of the cell. The 

 axone usually emerges from the middle of the basal surface, 

 and runs toward the medullary substance. It gives off many 

 collaterals on the way which run parallel to the surface. 



3. Large Pyramidal Cell Layer. This is made up of cells 

 quite similar in general form to those of the layer just de- 

 scribed. They are, however, much larger, especially in the 

 motor area of the cortex. The axones of these cells in part 

 enter the pyramidal tracts of the cord. 



4. Layer of Polymorphous Cells. In this layer we find 

 polygonal cells, which give off dendrites, and send axones into 

 the white matter. There are found also spindle-shaped cells 

 in this region. These cells, which are typical for individual 

 layers, and send their axones far beyond the cortex, are known 

 as Golgi cells type I. In addition there are numerous cells 

 whose axones never reach outside the limits of the cortex, and 

 end not far from the cell body. These are known as Golgi 

 cells type II. Some of these cells send their axones toward the 

 molecular layer, instead of toward the white matter, and jnv 

 known then as cells of Martinotti. 



The various layers are made up not only of cells, but contain 



