THE CENTRAL NERVOUS SYSTEM. 8 1 



the cerebral hemisphere, but, whatever the local modifications, the 

 general plan is the same in all parts, and shows an arrangement in 

 five layers (fig. 24). These layers are named as follows : 



(1) The outer fibre lamina, or molecular layer. 



(2) The outer cell lamina. 



(3) The middle cell lamina, or granule layer. 



(4) The inner fibre lamina. 



(5) The inner cell lamina, or layer of polymorphic cells. 



A convenient modification of this description is to speak of the 

 layers in their relation to the middle cell lamina or layer of granules. 

 This arrangement gives (1) a supragranular layer, consisting of a fibre 

 lamina and a cell lamina ; (2) the granule layer itself ; and (3) an 

 infragranular layer, consisting of a fibre lamina and a cell lamina. 



The outer fibre lamina contains medullated nerve fibres running 

 horizontally, a few scattered nerve cells, and the dendrons of many of 

 the cells of the next layer. 



The outer cell lamina contains pyramidal nerve cells, arid may be 

 subdivided into layers of small, medium, and large pyramids, the 

 small pyramids being most superficial, and the large pyramids most 

 deeply situated. 



The middle cell lamina contains pyramidal cells, but is especially 

 characterised by the presence of a large number of stellate cells, some 

 of which are large and others small. 



The inner fibre lamina consists of medullated nerve fibres, running 

 horizontally, but in the motor area it contains also large and often 

 solitary pyramidal nerve cells, called Betz cells, the apical dendrons of 

 which may extend to the outer fibre lamina. 



The inner cell lamina contains a large number of irregular or poly- 

 morphic cells, as well as some pyramidal cells, the cells of Martinotti, 

 the apices of which point centrally, while the axons pass towards the 

 surface. 



The Functions of the Cell Layers. Information may be obtained 

 as to the function of the different cell layers of the grey matter in 

 three ways: (1) by observing the order of their development in the 

 child ; (2) by a comparison of their relative proportion in man and 

 in the lower animals ; and (3) by a comparison of the different regions 

 in the human adult cerebrum, and by observations of the differences in 

 persons suffering from amentia or dementia. 



(1) The study of development of the cortex snows that the inner 

 cell lamina is the first to appear, and that it has attained three-fourths 

 of the adult depth at the sixth month of foetal life. It is followed by 

 the middle cell lamina, which, however, has only one-half of the adult 



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