THE CORP (IS CALLOSUM. 541 



rounded on all sides by the grey matter which is seen to follow closely 

 the convoluted surface, and to be of nearly equal thickness at all points. 

 This white central mass in each hemisphere was named by Vicq-d'Azyr 

 centrum ovale minus. On separating the remaining portions of the two 

 hemispheres from each other, two sulci are seen to exist between the corpus 

 callosurn and the gyri immediately in contact with it, viz., the gyrus 

 fornicatus of each side. These sulci were distinguished by the older anatomists 

 as ventricles of the coitus callosum. 



Another section being made at the level of the corpus callosum, the 

 white substance of that part is seen to be continuous with the internal 

 medullary matter of both hemispheres : and the large white medullary mass 

 thus displayed, surrounded by the border of cortical substance, constitutes 

 what is generally described as the centrum ovale, of Vieussens. 



The corpus callosum or great commissure (trabs cerebri) is a white struc- 

 ture, with a length not quite half of that of the brain, and approaching 

 about two-fifths nearer to the front than the back of the hemispheres. It 



Fig. 370. 



Fig. 370. HORIZONTAL SECTION OP THE BRAIN SHOWING THE LATERAL VENTRICLES AND 

 THE FIFTH VENTRICLE OPENED (from Sappey after Vicq-d'Azyr). ^ 



1, the fifth, ventricle ; 2, the two laminse of the septum lucidum meeting in front of 

 it ; 3, lesser hippocampus of the posterior cornu ; 4, horizontal section of the posterior 

 swelling of the corpus callosum; 5, middle part of the fornix, where it has been separated 

 from the corpus callosum ; 6, posterior pillar of the fornix ; 7, hippocampus major 

 descending in the middle cornu ; 8, eminentia collateralis ; 9, lateral parts of the fornix ; 

 10, choroid plexus ; 11, tsenia semicircularis ; 12, corpus striatum. 



is about an inch in width behind, and somewhat narrower in front. Its 

 thickness is greater at the ends than in the middle, and is greatest behind, 



