THE CENTRAL NERVOUS SYSTEM. 



and represented by the fibres of the corpus callosum and of the 

 anterior commissure. 



3. The projection fibres, streaming from the entrance of the 

 brain-stalks, or cerebral peduncles, secondarily also from the basal 

 nuclei, to spread out in the various parts of the cerebral cortex and 

 thus constitute the conspicuous corona radiata. 



The association fibres consist of bundles of various length, 

 which unite : (a) adjoining convolutions, passing from the medulla 

 of one, beneath the intervening fissure, into the white matter of the 

 neighboring gyrus ; (6) adjacent convolutions, but not immedi- 

 ately adjoining ; (/) more distant parts of the hemisphere. 



The most important of these longer tracts are : 



1. The fasciculus uncinatus, connecting the inferior frontal 

 convolution with the uncinate gyrus of the temporal lobe. 



2. The fasciculus longitudinalis inferior, connecting the an- 

 terior part of the temporal with the apex of the occipital lobe. 



3. The fasciculus longitudinalis superior, connecting the 

 middle of the frontal partly with the occipital and partly with the 

 apex of the temporal lobe. 



4. The cingulum, extending along the corpus callosum within 

 the cingulate convolution. 



5. The fasciculus perpendicularis, connecting the inferior 

 parietal with the fusiform lobe. 



6. The fornix, connecting the uncinate process of the hippo- 

 campal convolution with the thalamus by means of the continuations 

 effected by the fimbria behind and the bundle of Vicq d'Azyr, from 

 the mammillary body to the thalamus, in front. 



The majority of the commissural fibres, which connect similar 

 regions on the two sides, take part in the formation of the great 

 transverse bridge, the corpus callosum ; these fibres, the pro- 

 longations of the axis-cylinder processes of the cortical ganglion- 

 cells or of the collateral processes derived from the projection fibres, 

 pass to all parts of the cerebral surface, with the exception, probably, 

 of the anterior portions of the temporal lobes and the olfactory 

 tracts, which parts are connected by the fibres of the anterior 

 commissure. On either side of the closely-packed bundles con- 

 stituting the immediate bridge the fibres spread out in a fan-like 

 course to reach their destination. 



The projection or peduncular fibres include many of the most 

 important tracts by means of which communication between the 

 presiding cortical centres and the more deeply lying nuclei and paths 

 is established. The bundles of the crusta on reaching the sub- 

 thalamic region become continuous with the internal capsule and 

 spread out into the conspicuous corona radiata. The fibres which 



