200 CENTRAL NERVOUS SYSTEM 



portions of the vermiform lobe. The superficial gray matter 

 of the vermis is connected by association fibers with the dentate 

 nucleus, and the dentate nucleus by the superior peduncle 

 with the opposite cerebral hemisphere. 



3. They may pass to the anterolateral ascending tract of 

 the same side after passing through cells of origin in the spinal 

 gray matter. They pass thus to the superior peduncle of the 

 cerebellum, and enter the gray matter of the superior worm. 



4. They may cross the middle line, after entering the cord, 

 through axons or collaterals in the anterior or posterior com- 

 missures and pass up one of the ascending tracts. 



5. They may pass from neuron to neuron in the gray matter, 

 passing out at various levels on the same or opposite sides of 

 the cord. t 



Efferent Paths from Brain. As the result of impulses reaching 

 the brain, efferent impulses may be aroused which may make 

 their way through the cord as follows : 



1. Through the direct or crossed pyramidal tracts. 



2. From the frontal part of the cerebral cortex, through 

 the anterior limb of the internal capsule to the gray matter 

 of the pons, and thence by way of the middle peduncle to the 

 cerebellum. 



3. From the occipital and temporal cortex, in the posterior 

 limb of the internal capsule, to the pontine gray matter, and 

 thus through the middle peduncle to the cerebellum. From 

 the cerebellum they may pass to the nucleus of Deiters, and 

 thence along the anterolateral descending tract to the anterior 

 horn cells of the cord. 



Paths of Motor and Cutaneous Impulses. Lesions involving 

 the pyramidal tract above the decussation of the pyramids 

 cause paralysis of the opposite side of the body, but if situated 

 below the decussation, a paralysis on the same side. The 

 resulting paralysis, however, in many animals is only temporary. 

 The motor area of the cortex may establish connections with 

 the other side of the brain through commissural fibers, and in 

 addition there are other corticospinal paths which can sub- 

 serve volitional movements. On the other hand, hemisections 

 of the cord in man and animals indicate that there is a sensory 

 decussation. This for pain and temperature takes place chiefly 

 in the cord. The paths for touch and muscular sense probably 



