THE CEREBRAL CORTEX 65 



Plate XXXVI. shows a fusiform cell (0 1 ) and a polygonal cell (c) of the Cajal type in the 

 superficial layer of the cortex. The polygonal cell has several dendrites coming off in various 

 directions and dividing into smaller branches, which diverge. It also has a single neuraxon, 

 very small in diameter, which passes downward into the surface layer and becomes horizontal 

 and gives off collaterals, which also take a horizontal course. These fibres never turn down- 

 ward to enter the deeper layers. These cells differ in all respects from glia cells, which 

 Golgi has shown to exist in large numbers in this layer. 



In all the plates it is evident that there are numerous horizontal fibres in this superficial 

 layer. These are well marked in its deepest portion, and are shown with great distinctness 

 in Plate XXXVII. Into the surface layer there are seen to pass (in Plates XXXVIII. and 

 XLII.) the termination of the apical processes of the pyramidal cells. These have the typical 

 dendrite appearance, being covered with granules, and branching and dividing as they ascend. 

 These dendrites appear to end in free extremities in the superficial layer, there coming into 

 contact with the nerve fibres already described. 



Plate XXXVII. shows the triangular variety of Cajal cells (6). It also shows the fine 

 interlacing fibres of this layer. The origin of some of these fibres has already been described. 

 There are others which require to be noticed. It has already been stated that the neuraxons 

 ascending to the cortex from the spinal cord, the medulla, the cerebellum, and the basal 

 ganglia terminate in fine brush-like expansions in the cortex. It is in this layer of the cortex 

 that many of these terminal brushes lie. Hence this layer of the cortex certainly receives 

 impulses of many kinds from various parts of the lower nervous centres. It also receives 

 impulses from other regions of the cortex by means of fibres whose terminal expansions have 

 been traced to this layer. Thus the fibres of association from adjacent or distant pyramidal 

 cells end here, as do also many of the collateral fibres coming off from the neuraxons of 

 pyramidal cells in the layer just beneath the superficial layer, and also the neuraxons of 

 certain cells which pass directly to this layer; viz. the Martinotti cells. 



If, as Cajal and Van Gehuchten believe, it is the function of the branches of the apical 

 processes of the pyramidal cells of the second and third layers of the cortex to collect 

 impulses and convey them to their cells, it is evident that in the superficial layer of the 

 cortex they can receive such impulses from the most diverse and far separated parts of the 

 central nervous system. 



1 These letters refer to the cells shown in the diagram Fig. 10 on p. 72. 



