284 INNERVATION. [CHAP. X : 



portion, therefore, of the white substance of the hemispheres, the 

 centrum ovale, consists of fibres which establish a communication 

 between the gray undulating surface and these central garigliform 

 bodies. 



We are unable, however, to state that all the fibres of the 

 convolutions take this inward direction. Some of them, it has 

 been asserted, pass from convolution to convolution, uniting those 

 immediately adjacent, as well as the more remote. Such fibres, did 

 they exist, would pass at right angles to those above described, 

 and parallel to the gray surface. They would constitute intergyral 

 commissures. But the existence of such a series of fibres rests 

 on a foundation too uncertain to warrant us in speaking confidently 

 respecting it. When a brain which has been hardened by long 

 immersion in alcohol is torn along the surface of the convolutions, 

 the torn surfaces take on a fibrous appearance. But nothing of 

 the kind can be shewn in the fresh brain, in which the direction 

 of the fibres which converge to the corpora striata may be as easily 

 demonstrated as upon the hardened one. 



The gray matter of the convolutions does not exhibit an uniform 

 colour throughout its entire thickness. Much depends, as regards 

 the depth of colour of the whole layer, upon the quantity of blood 

 in its vessels. Compare the gray matter of an anaemic brain with 

 that of a healthy one, or, still more, of a congested one, and the 

 difference cannot fail to strike the most superficial observer. The 

 external portion has the darkest colour, and the internal in general 

 the lightest. In some convolutions, however, the intermediate 

 layer is white, and appears on the section like a white line sepa- 

 rating the inner from the outer layers. This is very obvious in 

 the convolutions forming the exterior of the descending horn of the 

 lateral ventricles. This white layer contains fine nucleus-like par- 

 ticles, similar to those which form the intermediate layer of the 

 gray matter of the cerebellum ; a coincidence of structure between 

 certain convolutions of the brain, and the gray matter of the cere- 

 bellum, which, doubtless, is not without some physiological sig- 

 nificance. 



Certain systems of fibres exist in the cerebrum, which seem 

 very evidently to unite portions of the same, or of opposite hemi- 

 spheres. The most obvious of these commissures are, the corpus 

 callosum, the anterior commissure, the posterior commissure, the soft 

 commissure, the superior longitudinal commissure, and the fornix. All, 

 except the two last, are transverse, and unite parts of the hemi- 

 spheres of opposite sides. 



