326 



NORMAL HISTOLOGY. 



THE WHITE MATTER OF THE CEREBRUM. 



The parts of the cerebrum thus far considered have included areas 

 composed chiefly of gray substance ; it remains to notice briefly the 

 complex mass of nerve-fibres forming- the conspicuous medulla. 

 It has already been stated that the nerve-fibres constituting these 

 central masses are mostly medullated, but devoid of a neuri- 

 lemma ; the fibres vary in diameter, those pursuing an extended 

 course connected with the large motor cells possessing, in general, 

 a greater diameter than those related with sensory areas. 



The accurate determination of the arrangement of the various 

 nerve-tracts included within the medulla is a labor of great difficulty 

 and one still far from satisfactory completion ; notwithstanding the 

 great advances made in this field of investigation since the introduc- 



FIG. 350. 



Diagram of association fibres of cerebrum: s, short fibres connecting adjacent gyri ; f.l.s., 

 superior longitudinal, f.l.i., inferior longitudinal, f.u , uncinate, and/!/., perpendicular fasciculus ; 

 ci, cingulum ; fo, fornix ; fi, fimbria ; v.d'A ., bundle of Vicq d" Az> r. (After Schae/er-Mtynert.) 



tion of the improved methods (Weigert's) for tracing medullated 

 fibres, much remains to be learned regarding the course and the 

 distribution of many tracts connecting the central nuclei with the 

 cerebral cortex. 



The great mass of the cerebral medulla is composed of fibre- 

 tracts, which may be grouped into three systems : 



1. The association fibres, connecting parts of the same hemi- 

 sphere. 



2. The commissural fibres, uniting parts of the two hemispheres, 



