500 



THE NERVOUS SYSTEM. 



external to all these structures is the island of ReiL The cortical 

 substance is at this point very near the gray matter of the basal 

 ganglia. 



The fibers of the internal capsule, passing upward, radiate 

 forward, upward, and backward, forming the corona radiata, the 

 fibers of which pass to the cortex, each one being the continuation 

 of the axis-cylinder process of a pyramidal cell. The fibers of 

 the internal capsule give off collaterals which pass to the optic 

 thalamus, and the nucleus caudatus and nucleus lenticularis of 



per. 



AF 



FIG. 291. Diagram to show the connection of the frontal occipital lobes with the 

 cerebellum: ec., the dotted lines passing in the crusta (TOO), outside the motor 

 fibers, indicate the connection between the temporo-occipital lobe and the cerebel- 

 lum ; F. C., the frontocerebellar fibers, which pass internally to the motor tract in 

 the crusta ; I.F., fibers from the caudate nucleus to the pons ; Fr., frontal lobe ; Oc. t 

 occipital lobe ; AF., ascending frontal ; AP., ascending parietal convolutions ; PCF., 

 precentral fissure in front of the ascending frontal convolution ; FR., fissure of 

 Eolando ; IFF., iuterparietal fissure. A section of crus is lettered on the left side : 

 S.IV., substantia nigra ; PY., pyramidal motor fibers, which on the right are shown 

 as continuous lines converging to pass through the posterior limb of /. C., internal 

 capsule (the knee or elbow of which is shown thus (*) ) upward into the hemisphere 

 and downward through the pons to cross at the medulla in the pyramidal decussa- 

 tion ; Ipt., crossed pyramidal tract; apt., direct pyramidal tract (Gowers). 



the corpus striatum. These ganglia give off fibers which pass 

 into the internal capsule and corona radiata. There are, there- 

 fore, fibers passing into these ganglia and others passing out 

 from them, the latter being the more numerous. The pyramidal 

 fibers in their downward course thus give off collaterals which 

 arborize around the cells of the corpus striatum and optic thala- 

 mus, and from these ganglia axis-cylinder processes pass out to 

 form a part of the pyramidal tract. So, also, the sensory fibers, 

 particularly those of the fillet, arborize around the cells of the 

 optic thalamus and the subthalamic region. 



