THE CEREBRAL HEMISPHERES. 



691 



fied, in all instances, by the facts, in view of the inevitable difficulty and uncertainty of 

 some of the processes employed ; and the graphic and admirable delineations by which 

 the work is illustrated, though professedly schematic, present a degree of ideality which 

 inspires some distrust with regard to the accuracy of the general conclusions. According 

 to Luys, the fibres of the encephalon have several directions, as follows : 



The gray matter of the cerebral hemispheres, as we shall see farther on, is composed 

 of a mass of nerve-cells, connected together by their prolongations into a plexus, which, 

 in its turn, is connected with the fibres of the white substance. From this cortical cellu- 

 lar plexus, white fibres arise, which may be divided, according to their direction and 

 destination, into two classes : The first class consists of curved commissural fibres, which 

 pass into the white substance to a certain depth and return to the gray matter, connect- 

 ing thus the gray substance of adjacent convolutions. The existence of these fibres 

 and their direction are well established. The second class consists of fibres which, 

 arising from the gray substance of the convolutions, connect these with the corpora 

 striata and the optic thalanru These may be called the converging fibres; and their 

 general direction, as far as it has been ascertained, is as follows : 



FIG. 226. Diagrammatic representation of tlie direction of the fibres in the cerebrum. (Le Bon.) 



Arising from the internal, concave surface of the cortical substance of the cerebrum, 

 the converging fibres, at first running side by side with the curved commissural fibres, 

 separate from the latter as they curve backward to pass again to the cortical substance, 

 and are directed toward the corpora striata and the optic thalami. The limits of the 

 irregular planes of separation of the commissural and the converging fibres contribute to 

 form the boundaries of the ventricular cavities of the brain. If we study the course of 

 the converging fibres arising from all points in the concave surface of the cerebral gray 

 matter, we find that they take various directions. The fibres from the anterior region of 

 the cerebrum pass backward and form distinct fasciculi which converge to the gray sub- 



