THE CEREBRUM. 



795 



In the middle of each hemisphere, the white substance constitutes a consider- 

 able nucleus, which, from its form, is named the centrum ovale (Vicq-d'Azyr) 

 (Fig. 427, 1 ; 434, 1), and which is united to that of the opposite side by the 

 great cerebral commissure, or corpus callosum, sending a prolongation into each 

 convolution ; thus exhibiting the exact disposition of the lateral white masses of 

 the cerebellum, with which the nuclei of the hemispheres have also another point 

 of resemblance, in that they are attached to the cerebral peduncles, as the first 

 are to the cerebellar. But the latter peculiarity is less evident than the others — 

 which are at once obvious in horizontal and transverse sections of the brain — 

 and can only be clearly demonstrated by the manipulations necessary to unravel 

 the intimate texture of the white substance. 



In studying this texture in brains hardened by nitric acid, washed in pure 

 water, and exposed to dry air for a day or two, we perceive that the white 

 cerebral substance is entirely composed of fine fibrous lamellae, diverging in every 



Fig. 438. 



Fi£r. 439. 



DIAGRAM OF THE COURSE OF THE ASSOCIATION 

 NERVE-FIBRES OF THE CORPUS CALLOSUM AND 

 OF THE ANTERIOR COMMISSURE. 



DIAGRAM OF THE COURSE OF THE RADIAT- 

 ING NERVE-FIBRES OF THE CORONA 

 RADIATA, AND THE RELATIONS OF THE 

 CORPORA STRIATA WITH THE CORTICAL 

 GREY SUBSTANCE. 



direction, corresponding by their concentric extremity to the centre of the 

 hemisphere, and abutting, by their peripheral extremity, on the inner face of the 

 grey covering of the convolutions. 



With regard to the relations between the centrum ovale and the cerebral 

 isthmus, and those the fibres of the former have with the other parts of the brain, 

 it is found that the fibres of the lower stage of the peduncles attach the 

 isthmus to the cerebral hemispheres, in passing through the corpora striata, and 

 radiate in the centrum ovale. Here these fibres form a kind of fan — the radiant 

 crown {corona radiata) of Reil. The internal capsule is the point of departure 

 of these fibres, and is therefore designated t\iQfoot {pes) of the radiant croivn. 



In the centrum ovale, the nerve-fibres form two great apparatuses — an 

 apparatus of association and an apparatus of radiation (Pitres). 



The first comprises a system of intra-hemisphere commissures, and a system of 

 inter-hemisphere commissures. 



The fibres of the first system unite the neighbouring convolutions, and those 

 more or less distant from each other. 



