250 



NORMAL HISTOLOGY. 



tributed in the gray matter of the cortex of the opposite hemisphere, 

 but not necessarily to the corresponding region. These commissural 



FIG. 232. 



Centrifugal and commissural fibres of the cerebrum. (R. y Cajal.) A, corpus callosum ; B, 

 anterior commissure ; C, pyramidal tract ; a, large pyramidal cell, with a neurite sending 

 a large collateral into the corpus callosum and then entering the pyramidal tract. 

 Between a and 6 is a second similar cell, the neurite from which contributes no branch 

 to the corpus callosum. 6, small pyramidal cell giving rise to a commissural neurite ; c, a 

 similar cell, the neurite of which divides into a commissural and an association branch ; 

 d, collateral entering the gray matter of the opposite hemisphere ; e, terminal teleneu- 

 rites of a commissural fibre. 



fibres give off collaterals, which also end in the gray matter, and 

 are accompanied by collaterals from the centrifugal fibres, which 

 likewise end in, and send collaterals to, the gray matter. 



FIG. 233. 



Association-fibres of the cerebrum. (R. y Cajal.) The figure represents, diagrammatically, 

 a sagittal section through one of the cerebral hemispheres, a, pyramidal cell, with neu- 

 rite giving off collaterals to, and ending in, the gray matter of the same side ; b, a similar 

 cell ; c, cell with a branching neurite passing to different parts of the hemisphere ; d, 

 teleneurites ; e, terminal collateral twigs. 



The origin, course, and general distribution of the association- 

 fibres are indicated in Fig. 233. They are so numerous that they 



