Hatai, Cerebral Cortex. 203 



Tliis fourth layer in the aduh human cortex stained with Golgi's 

 method reveals many cells (cells of Martinotti), the main den- 

 drites of which run towards the ventricles, while the axone goes 

 towards the surface of the cortex, thus exhibiting the arrange- 

 ment at maturity which this method of development would lead 

 us to expect. 



The studies on the fifth layer furnish still stronger evidence. 

 In this layer the direction of the main processes is exactly the 

 same as in the third layer; that is, the processes turn towards 

 the surface of the cortex. The only differences between these 

 two layers just mentioned, are (i) shortening of the long dia- 

 meter of the nucleus, (2) enlargement of the cell as a whole. 

 Besides these important differences we observe the formation 

 of the new processes from the base of the cell-body. This basal 

 process newly developed, is extremely slender and similar in 

 character to the corresponding process in the fourth layer. 

 Partly or completely rotated cell-bodies are observed, but the 

 number of such cells is very small; a single field (oc. 4 X obj. 

 I- 1 2 B. L.) containing one or two or sometimes none of these 

 cells. Thus we can say that the direction of the main den- 

 drites is the same in both earlier stages and in the adult; that 

 is, rotation does not take place in this layer, and the main pro- 

 cess which was produced first from the cell-body is a dendrite, 

 the neuraxone appearing later. This is shown also in Fig. 3, 

 where the cells already have their main processes, while the basal 

 process or neuraxone is as yet only slightly developed. Paton 

 ('00), who noticed a similar appearance in the cortical layer of 

 the foetal pig, said "The process (main process or dendrite), 

 apparently continuous with the nucleus, can be followed often 

 well into the superficial layer. I do not believe that at this 

 period the neuroblasts have any basal process or axone." 



These observations apply also to the cortical layers of the 

 foetal rat. The developmental history of the neurone in this 

 animal is quite similar to that in the cat, and therefore there is 

 no necessity to describe the rat cortex in detail. 



