380 CORPUS CALLOSUM. 



The proportion of this medullary part is much greater than 

 that of the cortical. The cortical, however, surrounds it, so as 

 to form the whole of the surface of the cerebrum, that can be 

 strictly said to be exterior. 



The color of the cortical part appears to be derived from 

 the blood ; as its intensity seems regularly proportioned to the 

 quantity of blood in the head. In subjects who have been 

 plethoric, or have had a detertnination of blood to the head ; it 

 is uniformly high-colored ; in pallid and exhausted subjects it is 

 of a fainter color. 



The medullary matter is uniformly white ; but small red 

 points appear upon its surface, when cut, which are the sec- 

 tions of vessels which carry red blood ; and these points are 

 larger and more numerous in plethoric, than in exhausted 

 subjects. It is rather firmer than the cortical substance. 



These two substances are most intimately connected in the 

 cerebrum, and indeed seem to be a continuation of each other. 

 In some parts they are blended together ; and in other places, 

 there are portions of cortical matter within the medullary. 



The division of the cerebrum into two hemispheres extends 

 to a considerable depth from above, and also to a considerable 

 distance internally, from its anterior and posterior extremities ; 

 of course, the part which is undivided is in the centre. 



The cortical part covers also the surfaces, which are in the 

 great fissure that forms the two hemispheres, and is occupied, 

 in a great degree, by the falciform process of the dura mater. 

 Towards the bottom of this fissure, and below the falx, these 

 surfaces being opposed to each other, and in contact, are slight- 

 ly united by adhesion of the membranes that cover them. 



The central part, which is not divided, and which must 

 appear at the bottom of the fissure, when the two hemispheres 

 are separated from each other, is medullary ; being evidently 

 a union of the medullary matter of each hemisphere. This 

 undivided medullary part is equal to about one half of the 

 length of the hemispheres ; the fissures at each extremity ex- 

 tending inwards, about one-fourth of their length. On each 

 side of it, a fissure, equal to it in length, extends horizontally 



