658 



STRUCTURE OF THE CEREBRUM 



[cir. XLVL 



2. The layer of pyramids. There are several deep, and the largest 

 cells are situated most deeply. Each of these has an apical process 

 running to the surface, where the branches run tangentially. The 

 lateral processes are also branched dendrons. The axon originates 

 from the base. The largest pyramids (Betz cells) are found in the 

 so-called motor cortex (Rolandic area) and give origin to the fibres 

 of the pyramidal tract. The smaller pyramids are association units. 



3. The layer of polymorphous cells. There are small scattered 

 cells, many of a fusiform shape. In the Island of Eeil this layer is 

 hypertrophied, and is separated from the rest of the grey matter by 

 a stratum of white fibres ; it is known then as the daustrum. 



Variations in different regions of the cortex will be found described 



Fia. 480. Human cerebral cortex : Golgi's method. Low power. (Mott.) 



in histological works, but the physiological meaning of these is not 

 clear in many cases. The Golgi method has proved conspicuously 

 useful in the study of the shapes and dispositions of the cells (see 

 figs. 479, 480, 481). Bundles of medullated nerve-fibres pass in vertical 

 streaks through the deeper layers of the grey matter ; some of these 

 are axis cylinder processes of the pyramidal and polymorphous cells, 

 and are conveying impulses downwards ; others conveying impulses 

 upwards pass from the white matter into the cortex to arborise among 

 its various cells. In addition to these fibres, other strands lie parallel 

 to the surface of the cortex, and have received various names, such as 

 the outer line of Baillarger in the layer of medium-sized pyramids, 

 the inner line of Baillarger in the layer of large pyramids, and the 



