LECTURE V. 



THE CORTEX OF THE FORE-BRAIN, THE WHITE SUBSTANCE OF THE 

 HEMISPHERES, THE COMMISSURES, AND THE CORONA RADIATA. 



GENTLEMEN : In the previous lecture you were taught the 

 appearance of the surface of the brain, the fissures which traverse 

 it, and the convolutions situated thereon. 



To-day's lecture is intended to give you a more intimate 

 knowledge of the structure of the cortex, and to place before 

 you a general view of the connections of the various cortical 

 regions with one another and with the deeper-lying structures. 



We know the elements only which go to make up the 

 finer structure of the cortex. The actual connections between 

 these elements are still hidden from us, and therefore, unfortu- 

 nately, we are deprived of the very essentials for a correct un- 

 derstanding of the anatomical substratum of the great organ of 

 the mind. There is scarcely a doubt but that the cortex, taken 

 as a whole, may be regarded as the region where most of the 

 conscious mental processes take place ; that in it is the seat of 

 thought, and that from the cortex all conscious voluntary acts 



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proceed. The whole hemisphere is covered by the cortex. 

 however, has not the same structure at all points of the 

 vexity, and although we can make out a sort of fundamental - 

 type, yet there is a wide departure from this type in different 

 parts of the cortex, particularly in those layers which contain 

 the ganglion-cells and nerve-fibres. One structural type never 

 passes abruptly into another. Inasmuch as the significance of 

 these anatomical variations is unknown, let us to-day only con- 

 sider the cortex of one region, of the frontal lobe. Here, 





under the pia mater, lies a layer of neuroglia with numerous 

 glia-cells. It contains a thick net- work (1 in the. accompanying 



(63) 



