COETES OF FOBEBEAIN AND MEDULLA OF HEMISPHEEES. 231 



The outermost layer contains numerous nerve-fibers running, for the moat part, 

 in a tangential direction. These arise from ganglionic cells {a, 6, and c), all of 

 which possess several neuraxons, and from small fusiform cells {d) of a deeper layer. 

 Two kinds of elements enter this outermost zone. Large fibers (e), mostly meduUated, 

 which pass into the cortex from the medullary layer, are traced in their outermost 

 ramifications into this layer. They must originate from ganglionic cells that lie 

 in other parts of the brain. The caliber of the fibers speaks especially for a distant 

 origin. Then the dendrites of the more deeply situated pyramidal cells {f) end in this 

 layer in dense, profuse ramifications. Numerous fine secondary twigs, terminating in 

 little knobs, project from each of the small branches. The ramification is so dense 

 that exceedingly abundant opportunity is afforded for the contact of the dendrites 

 of deep cells with similar dendrites and the neuraxons of cells lying in this locality. 

 Even the most daring phantasy of speculative psychologists has hardly allowed itself 

 to imagine such an abundance of possible combinations as has here been revealed 

 of the dendrites with neuraxons of cells which have very different locations. 



And, moreover, every cell is, and remains, an independent individual, not here 

 only, but everywhere else in the cortex. Direct union is nowhere recognized; con- 

 nection by contact alone is observed throughout. 



The layer of small pyramidal cells lies under the layer of tangential fibers. 

 It passes very gradually over into the layer of the large pyramids (3). The neu- 

 raxons of all these cells pass in a direction toward the medullary layer; they give 

 off numerous collaterals. Many neuraxons divide near the medullary layer into a 

 horizontal and a descending branch. From these fibers arise the tracts which con- 

 nect the cerebral cortex with deeper-lying centers and which connect distant cortical 

 centers with one another. 



The dendrites extend a, greater or less distance out toward the periphery, and 

 some of them end only under the pia. 



Near the medullary layer, below the well-defined pyramids, lie numerous irregu- 

 larly triangular, also small pyramidal, cells. As regards the course of their neu- 

 raxons, as well as their dendrites, they are analogous to the pyramids, but they 

 present more irregular forms and a less dense ramification. In this deepest layer are 

 found numerous multipolar cells {g) , the neuraxons of which may run in the most 

 various directions: horizontal, ascending, descending, etc. The neuraxon is always 

 characterized by the fact that, after a short course, it breaks up into a wide, com- 

 plicated arborization, the terminal fibrils of which all end freely. Moreover, such 

 cells are also present in almost all of the other layers of the cortex. With their 

 extensive ramification, they are well adapted to connect other cell-groups with one 

 another physiologically. 



The innumerablG neuraxons with their collaterals and the numerous 

 fibers passing into the cortex from other parts of the brain together form, 

 as would be expected, an extraordinarily dense net-work. It was only pos- 

 sible to untangle this complex through the happy circumstance that the 

 method of Golgi always impregnates, at the most, relatively few cells in any 

 one section. The same net-works of fibers, as shown in Fig. 151 by the 

 myelin-staining method, may be demonstrated with the staining of the cells, 

 but in the latter case they are miieh more compact and solid. It appears 

 that the neuraxons of most of the cells in the cortex, and the collaterals, also, 

 which arise from the neuraxons of the pyramids, possess a medullary sheath. 



