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STRUCTURE OF THE CEREBRUM 



[CH. XLVIII. 



The cortex may be divided into five primary laminae : 



1. The outer fibre layer or superficial lamina. The fibres are 

 largely derived from the dendrons of the cells of the next layer. The 

 nerve-cells (F in fig. 433) intermingled with these are branched, and 

 have several processes which lie horizontally beneath the surface 

 (tangential fibres). There are doubtless association units linking 

 the incoming afferent neurons to those which are motor. Neuroglia 

 cells are also present. 



2. The outer cell lamina or layer of small 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 



FIG. 434. Human cerebral cortex : Golgi's method. Low power. (Mott.) 



dendrons. The axon originates from the base. The layer of small 

 pyramids increases in depth as we ascend the animal scale. They 

 are believed to be association units subserving the higher mental 

 processes. 



3. The middle cell lamina (numbered 4 in figure 432). This 

 consists of small cells called granules. This layer is a distinguishing 

 mark of sensory areas, and is practically absent in the pre-Eolandic 

 or motor convolutions. 



4.^ The inner fibre layer. In certain regions of the cortex this 

 contains the giant pyramids or Betz cells, which are characteristic 

 of the motor areas. In the visual cortex the so-called solitary cells 

 of Meynert are present here. 



