THE NERVOUS SYSTEM 491 



ganglion, enter the spinal cord, and reach the medulla by the 

 dorsal columns of the cord. In the dorsal columns of the cord 

 they travel on the side they enter, and finally reach the medulla 

 in the gracilis and cuneate nuclei, where they arborise. Through 

 the fresh fibres there formed the impulses cross to the other side 

 of the medulla, and by means of the fillet reach the mid-brain 

 and optic thalamus. From the thalamus the fibres are dis- 

 tributed by means of the internal capsule to that portion of 

 the cerebral cortex not occupied by the motor areas in front 

 and behind the fissure of Rolando. Impulses which, though 

 afferent, are probably not sensory, but for reflex work, gain the 

 medulla via Clarke's column. The spinal roots on entering 

 the cord arborise around the cells in this column, and by 

 means of the fibres forming the dorsal and ventral cerebellar 

 tract they reach the brain as follows. The dorsal (direct) 

 cerebellar tract passes by means of the restiform body into the 

 superior part of the vermis, while the ventral cerebellar tract 

 runs along the lateral columns to the pons, passes beneath the 

 roots of the fifth nerve, and then bends back to end in the 

 superior vermis of the cerebellum. It is by means of the lateral 

 columns that pain-provoking impressions are conveyed from 

 both halves of the body. These impulses having reached the 

 pons, they pass to the optic thalamus, which is the sensory relay 

 station to the cortex and the seat of pain. 



The Association System of fibres is employed in bringing the 

 various parts of the brain into connection — convolution with 

 convolution, lobe with lobe, cerebrum with mid-brain, cere- 

 bellum, and pons. Some fibres, the commissural, connect 

 the right side with the left in all its anatomical parts, the 

 corpus callosum being the largest member of this system. The 

 system of association fibres links up the various parts of the 

 brain and affords routes innumerable for the passage of impulses 

 to and fro. It has been previously mentioned that the complexity 

 of the dendrites of the cells bears some relation to the scale of 

 brain development in the animal kingdom ; it may now be noted 

 that the more profusely branched the dendrites the larger the 

 number of paths there are in the association system. 



Functions of the Cerebrum. 



The cerebrum is without sensation ; it can be handled, cut, or 

 otherwise injured without any sign of pain being elicited. For 

 many years it was considered, in consequence of the experiments 

 of Flourens, that the cerebrum was a homogeneous organ, 

 and all of its parts functionally of the same character. It was 

 known to be connected with the higher faculty of intelligence, 



