THE CENTRAL NERVOUS SYSTEM 685 



the optic thalamus and the region below it (sub-thalamic 

 region) by forming synapses with nerve- cells, whose axons, 

 passing through the posterior limb of the internal capsule 

 and the corona radiata, continue the afferent path to the 

 cerebral cortex. A few of the fibres of the mesial fillet may, 

 however, run straight on to the cortex without being inter- 

 rupted by nerve-cells. 



Some of the internal arcuate fibres, instead of passing into 

 the fillet after crossing the middle line, bend out (as external 

 arcuate fibres) along the edge of the anterior median fissure., 

 and coursing superficially around the pyramid and olive, reach 



FIG. 249. DIAGRAMMATIC TRANSVERSE SECTION OF CRURA CEREBRI AND 

 AQUEDUCT OF SYLVIUS. 



a, anterior corpora quadrigemina ; b, aqueduct ; c, red nucleus ; d, fillet ; e. sub- 

 stantia nigra ; /, pyramidal tract in the crusta of the crura cerebri ; g, fibres from 

 frontal lobe of cerebrum ; h, fibres from temporo-occipital lobe ; i, posterior longi- 

 tudinal bundle. 



the restiform body. A connection is thus established between 

 the two nuclei and the opposite side of the cerebellum. 

 Numerous fibres also go directly from the nuclei, and especially 

 the nucleus cuneatus, to the restiform body of the same side. 

 Connections of the Pyramidal Tracts. When the cortex 

 around the fissure of Rolando is destroyed by disease in 

 man, or removed by operation in animals, it is found that in 

 a short time degeneration has taken place in the fibres of the 

 corona radiata which pass off from this area. The degenera- 

 tion can be followed down through the genu and the anterior 



